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Heart and Great Vessels - Complete Anatomy Notes

Sources: Gray's Anatomy for Students, Color Atlas of Human Anatomy Vol. 2 (Internal Organs), Goldman-Cecil Medicine

1. OVERVIEW AND GENERAL FEATURES

The heart is a hollow, muscular pump located in the mediastinum of the thoracic cavity. Its shape resembles a pyramid that has fallen over and rests on one of its sides. The heart has:

Weight: ~250-350 g in adults
Size: Roughly the size of the owner's fist
Location: The middle mediastinum, enclosed within the pericardial sac

2. ORIENTATION, SURFACES, AND BORDERS

Orientation

The heart rests on its diaphragmatic surface, with:

Apex pointing forward, downward, and to the left (left 5th intercostal space, 8-9 cm from the midsternal line)
Base directed posteriorly, fixed to the pericardial wall opposite vertebral bodies TV-TVIII (TVI-TIX standing)

Surfaces

Surface	Composition
Anterior (sternocostal)	Mostly right ventricle; right atrium on the right, left ventricle on the left
Diaphragmatic (inferior)	Left ventricle (majority) + small portion of right ventricle; separated by posterior interventricular groove
Left pulmonary	Left ventricle + portion of left atrium; broad and convex
Right pulmonary	Right atrium; broad and convex
Base (posterior)	Left atrium (mostly) + small portion of right atrium + proximal great veins (SVC, IVC, pulmonary veins)

Margins

Right margin = Right pulmonary surface (right atrium)
Left margin (obtuse) = Anterior/left pulmonary surfaces; from left auricle to apex; formed by left ventricle
Inferior margin (acute) = Sharp edge between anterior and diaphragmatic surfaces; mostly right ventricle
Superior margin = Formed by the right and left atria and auricles

Radiological Borders (PA CXR)

Border	Structures
Right	SVC, right atrium, IVC
Left	Arch of aorta (aortic knuckle), pulmonary trunk, left auricle, left ventricle
Inferior	Right ventricle + left ventricle at apex

3. EXTERNAL SULCI

Internal partitions produce external grooves (sulci):

Coronary sulcus (atrioventricular groove): Circles the heart, separates atria from ventricles. Contains: right coronary artery, small cardiac vein, coronary sinus, and circumflex branch of the left coronary artery.
Anterior interventricular sulcus: Anterior surface; separates the two ventricles. Contains: anterior interventricular artery (LAD) and great cardiac vein.
Posterior interventricular sulcus: Diaphragmatic surface. Contains: posterior interventricular artery (PDA) and middle cardiac vein.

4. PERICARDIUM

The heart is enclosed in the pericardium, a double-walled sac:

Fibrous pericardium (outer): Tough, inextensible; attached to the central tendon of the diaphragm below and fusing with the adventitia of the great vessels above
Serous pericardium (inner): Two layers:
- Parietal layer: Lines the inner surface of fibrous pericardium
- Visceral layer (epicardium): Closely applied to the surface of the heart and great vessels
- Pericardial cavity: Potential space between the two serous layers, containing a thin film of serous fluid for lubrication

Pericardial Sinuses

Transverse sinus: Lies between the arterial vessels (aorta + pulmonary trunk) anteriorly and the venous vessels (SVC + pulmonary veins) posteriorly
Oblique sinus: A blind-ending recess behind the left atrium, bounded by the pulmonary veins

5. LAYERS OF THE HEART WALL

Layer	Description
Epicardium	Outer layer; mesothelium + thin connective tissue + subepicardial fat (visceral pericardium)
Myocardium	Middle; cardiac muscle; thickest in the left ventricle
Endocardium	Inner lining; continuation of the tunica intima of vessels; endothelium + thin connective tissue

Histology of Cardiac Muscle

Cells are up to 120 μm long, average diameter 20 μm in adults
Branched cells connected end-to-end; centrally placed pale nucleus
Intercalated discs: Transverse cell boundaries; contain desmosomes (mechanical coupling) and gap junctions/nexus (electrical coupling for impulse propagation)
T-tubules (transverse): Derivatives of the sarcolemma; involved in excitation-contraction coupling
L-tubules (longitudinal): Formed by the sarcoplasmic/endoplasmic reticulum
Rich in mitochondria (energy supply) and glycogen

6. CARDIAC SKELETON

A collection of dense fibrous connective tissue forming four fibrous rings in a plane between the atria and ventricles:

Surrounds all four valve orifices: two atrioventricular (mitral, tricuspid) + two arterial (aortic, pulmonary)
Functions: Provides attachment for cardiac muscle bundles; electrically insulates atria from ventricles (except the AV bundle); maintains shape of valve orifices
The only pathway for electrical conduction from atria to ventricles is the AV bundle (Bundle of His) passing through the central fibrous body

7. CHAMBERS OF THE HEART

7.1 Right Atrium

Two functional parts:

Sinus of the venae cavae (posterior, smooth-walled):

Receives the superior vena cava (SVC) - opens downward and anteriorly, no valve
Receives the inferior vena cava (IVC) - opening shielded by the valve of the IVC (Eustachian valve), a crescent-shaped fold; in fetal life this was large and directed blood through the foramen ovale
Foramen ovale (fetal) becomes the oval fossa (fossa ovalis) after birth, bordered by the limbus fossae ovalis
Receives the coronary sinus (returns deoxygenated blood from the heart wall), guarded by the valve of the coronary sinus (Thebesian valve)
Smallest cardiac veins (foramina of Thebesius) open directly into the right atrium

True atrium (anterior):

Interior: pectinate muscles (muscular ridges projecting into the cavity)
Continuous anteriorly with the right auricle
Separated from the sinus by the crista terminalis (internal ridge; externally the sulcus terminalis)

Interatrial septum: Contains the fossa ovalis; occasionally a patent foramen ovale (PFO) persists.

7.2 Right Ventricle

Two parts separated by muscular ridges:

Supraventricular crest (crista supraventricularis)
Septomarginal trabecula (moderator band)

Part	Location	Features
Inflow tract	Posteroinferior	Trabeculae carneae (muscular ridges); chordae tendineae; papillary muscles
Outflow tract (conus arteriosus/infundibulum)	Anterosuperior; smooth-walled	Leads to pulmonary trunk

Key structures:

Trabeculae carneae: Muscular ridges projecting into the cavity
Papillary muscles (3): Anterior (largest), posterior, septal - prevent eversion of tricuspid valve cusps during systole
Chordae tendineae: Tendinous cords connecting papillary muscles to valve cusps
Septomarginal trabecula (moderator band): Bridges the lower interventricular septum to the base of the anterior papillary muscle; carries the right bundle branch of the AV conduction system
Myocardial wall thickness: Thin (3-5 mm); produces lower pressure (pulmonary circulation)

7.3 Left Atrium

Forms most of the base (posterior surface) of the heart
Four pulmonary veins enter (two on each side) - no valves; the pulmonary vein ostia are smooth-walled (derived from incorporated pulmonary vein)
Interior: mostly smooth-walled (evolved from absorbed pulmonary veins)
Left auricle is a small appendage projecting anteriorly - in atrial fibrillation, thrombi commonly form here
Interatrial septum: The left side shows a slight depression at the fossa ovalis

7.4 Left Ventricle

Thickest-walled chamber (~8-12 mm vs. 3-5 mm of RV) - generates systemic arterial pressure

Two parts:

Inflow tract: Receives blood from left atrium through mitral valve; contains trabeculae carneae and two large papillary muscles (anterior and posterior), connected to mitral valve cusps by chordae tendineae
Outflow tract (aortic vestibule): Smooth-walled; leads to ascending aorta through the aortic valve

Interventricular septum: Has a thick muscular part and a thin membranous part superiorly (site of most VSDs).

8. HEART VALVES

Right Ventricle Interior showing valve anatomy

8.1 Tricuspid Valve (Right AV Valve)

3 cusps: Anterior, septal, posterior (named by position in RV)
Bases attached to the right fibrous ring (annulus fibrosus)
Cusps are continuous at commissures
Chordae tendineae attach the free margins to 3 papillary muscles
Prevents reflux into right atrium during ventricular systole

8.2 Pulmonary Valve (Semilunar)

Located at the apex of the infundibulum (outflow tract of RV)
3 semilunar cusps: Left, right, and anterior (named by fetal position before outflow rotation)
Each cusp has:
- Nodule (thickened middle of free edge)
- Lunula (thin lateral portions)
- Pulmonary sinus (pocket-like dilation in pulmonary trunk wall)
After ventricular contraction, blood recoil fills sinuses, forcing cusps closed

8.3 Mitral Valve / Bicuspid Valve (Left AV Valve)

2 cusps: Anterior (aortic/septal) and posterior (mural)
Bases attached to the left fibrous ring (annulus fibrosus)
Connected by chordae tendineae to two papillary muscles (anterior and posterior) in the LV
Prevents reflux into left atrium during ventricular systole

8.4 Aortic Valve (Semilunar)

Located at the junction of the aortic vestibule and ascending aorta
3 semilunar cusps: Right, left, and posterior (= non-coronary)
Each forms a pocket-like aortic sinus (sinus of Valsalva):
- Right aortic sinus → gives rise to the right coronary artery
- Left aortic sinus → gives rise to the left coronary artery
- Posterior (non-coronary) sinus → no coronary artery origin
After ventricular contraction, blood recoil fills the sinuses, closes the valve, and simultaneously forces blood into the coronary arteries

Valve Surface Landmarks (Auscultation Areas)

Valve	Anatomical location	Auscultation site
Aortic	Right 2nd intercostal space, parasternal	Right 2nd ICS
Pulmonary	Left 2nd intercostal space, parasternal	Left 2nd ICS
Tricuspid	Lower left sternal border	Left 4th/5th ICS, parasternal
Mitral	Left 5th ICS, midclavicular line	Apex (mitral area)

9. BLOOD SUPPLY - CORONARY ARTERIES

Coronary artery distribution - anterior and superior views

Coronary arteries arise from the right and left aortic sinuses of the ascending aorta. They lie in the subepicardial fat within the coronary and interventricular sulci. Functionally, they are end arteries (small anastomoses are insufficient to develop adequate collateral circulation acutely).

9.1 Right Coronary Artery (RCA)

Arises from the right aortic sinus
Travels in the coronary sulcus (right atrioventricular groove)
Branches:
- SA nodal artery (in ~60% of people from RCA; 40% from LCx)
- Right marginal artery (acute marginal)
- Posterior interventricular artery (PDA) - in right dominant circulation (~70% of people); runs in the posterior interventricular sulcus to supply the posterior 1/3 of interventricular septum
- AV nodal artery (usually from RCA in right-dominant hearts)
Supply (right-dominant): Right atrium, SA node (mostly), AV node, right ventricle (most), posterior portion of LV, posterior 1/3 of interventricular septum

9.2 Left Coronary Artery (LCA)

Short trunk (~1-2 cm = left main stem) arising from left aortic sinus
Passes between the pulmonary trunk and left auricle before bifurcating

A. Left Anterior Descending (LAD) / Anterior Interventricular Artery

Travels in the anterior interventricular sulcus toward the apex
Clinical name: LAD
Branches: Diagonal branches, septal perforating arteries
Supply: Anterior 2/3 of interventricular septum, anterior wall of LV, anterior wall of RV, apex

B. Left Circumflex (LCx) / Circumflex Artery

Runs posteriorly in the left coronary sulcus (left atrioventricular groove)
Branches: Obtuse marginal arteries
Supply: Left atrium, lateral and posterior wall of LV

Coronary Dominance

Dominance	Definition	Incidence
Right dominant	PDA from RCA	~70%
Left dominant	PDA from enlarged LCx	~10%
Co-dominant (balanced)	Both RCA and LCx contribute	~20%

Coronary Veins

Vein	Course	Empties into
Great cardiac vein	Anterior interventricular sulcus → left coronary sulcus	Coronary sinus
Middle cardiac vein	Posterior interventricular sulcus	Coronary sinus
Small cardiac vein	Right side of coronary sulcus	Coronary sinus
Coronary sinus	Posterior coronary sulcus	Right atrium (between IVC and TV)
Anterior cardiac veins	Anterior RV wall	Directly into right atrium
Smallest cardiac veins (Thebesian)	Heart wall	Directly into cardiac chambers

10. CONDUCTING SYSTEM OF THE HEART

Conduction system showing SA node, AV node, bundle of His, and bundle branches

Specialized cardiac muscle cells that generate and conduct rhythmic electrical impulses, differing histologically and functionally from the working myocardium.

Components

Structure	Location	Function
SA Node (Keith-Flack node)	Beneath epicardium at the junction of SVC and right atrium (near sulcus terminalis)	Primary pacemaker; generates ~60-100 impulses/min
Internodal pathways	Atrial myocardium	Conduct impulse from SA → AV node
AV Node (Aschoff-Tawara node)	Floor of right atrium near the opening of the coronary sinus; at apex of Koch's triangle	Delays impulse (~0.12 sec); allows atrial contraction to complete before ventricular contraction; backup pacemaker (~40-60/min)
Bundle of His (AV bundle)	Runs along the lower border of the membranous interventricular septum	Only electrical pathway between atria and ventricles (through the cardiac skeleton)
Right bundle branch	Descends on right side of interventricular septum → enters septomarginal trabecula → to anterior papillary muscle	Conducts to right ventricle
Left bundle branch	Passes to left side of muscular IVS → descends to apex	Conducts to left ventricle (divides into anterior and posterior fascicles)
Subendocardial plexus (Purkinje fibers)	Spread throughout ventricular walls (subendocardial)	Rapidly distributes impulse to ventricular myocardium including papillary muscles

Koch's triangle (boundaries): Tendon of Todaro posteriorly, septal leaflet of tricuspid valve anteriorly, coronary sinus ostium inferiorly - the AV node lies at the apex.

11. INNERVATION OF THE HEART

The heart receives autonomic innervation via the cardiac plexus:

Cardiac Plexus

Part	Location
Superficial	Inferior to the aortic arch, between it and the pulmonary trunk
Deep	Between the aortic arch and the tracheal bifurcation

Sympathetic Supply

Origin: T1-T5 lateral horn (sympathetic chain ganglia - cervical and upper thoracic)
Nerves: Cardiac accelerator nerves from the superior, middle, and inferior cervical sympathetic ganglia + thoracic cardiac branches
Effects: Increased heart rate (chronotropy), increased force of contraction (inotropy), coronary vasodilation, increased conduction velocity

Parasympathetic Supply

Origin: Dorsal motor nucleus of the vagus nerve (CN X)
Nerves: Superior and inferior cervical cardiac branches of the vagus nerve
Effects: Decreased heart rate, decreased AV conduction (primarily acts on SA and AV nodes), coronary vasoconstriction (minor effect)

Afferent (Pain) Fibers

Travel with sympathetic fibers → enter the spinal cord at T1-T5
Referred pain of cardiac ischemia: Left chest, left arm (ulnar aspect), left jaw, epigastrium - due to convergence of afferent fibers from these dermatomes at T1-T5

12. GREAT VESSELS

12.1 Aorta

Four parts:

A. Ascending Aorta

Rises from the aortic valve (at the level of sternal angle/T4)
Length: ~5 cm
Gives off the right and left coronary arteries (only branches of ascending aorta)
Enclosed within the pericardial sac

B. Arch of the Aorta

Begins after the pericardium; curves superiorly, posteriorly, and to the left over the left main bronchus
Ends at the level of the sternal angle (T4)
Branches from right to left:
1. Brachiocephalic trunk (innominate artery) - divides into right common carotid + right subclavian
2. Left common carotid artery
3. Left subclavian artery
Related to: ligamentum arteriosum (remnant of ductus arteriosus, connecting it to the pulmonary trunk), recurrent laryngeal nerves, cardiac plexus, trachea

Aortic isthmus: The slight constriction just distal to the origin of the left subclavian and proximal to the ductus arteriosus/ligamentum; site of coarctation of the aorta.

C. Descending Thoracic Aorta

From T4 to T12 (aortic hiatus of the diaphragm)
Branches: Posterior intercostal arteries (3rd-11th), subcostal arteries, bronchial arteries, esophageal arteries, superior phrenic arteries

D. Abdominal Aorta

From aortic hiatus (T12) to bifurcation at L4 into right and left common iliac arteries

12.2 Pulmonary Trunk

Arises from the right ventricle (infundibulum) at the pulmonary valve
Approximately 5 cm long; passes posterosuperiorly within the pericardium
Divides at the concavity of the aortic arch (below the carina, at T5) into:
- Right pulmonary artery - longer; passes to the right lung behind the ascending aorta and SVC
- Left pulmonary artery - shorter; connected to the aortic arch by the ligamentum arteriosum (obliterated ductus arteriosus)
Carries deoxygenated blood from the right ventricle to the lungs

12.3 Superior Vena Cava (SVC)

Formed by the union of the right and left brachiocephalic veins at the level of the right 1st costal cartilage
Length: ~7 cm; no valves
Descends on the right side, entering the right atrium at the level of the right 3rd costal cartilage
The lower half is within the pericardium
Drains venous blood from: head, neck, upper limbs, and thoracic wall (above the diaphragm)
The azygos vein drains into the SVC posteriorly at the level of the right hilum

12.4 Inferior Vena Cava (IVC)

Formed by the union of the two common iliac veins at the level of L5
Passes through the caval opening in the diaphragm at T8
Enters the right atrium from below
Guarded by the valve of the IVC (Eustachian valve) within the right atrium
Drains venous blood from: lower limbs, abdominopelvic organs, kidneys, gonads, liver (via hepatic veins)

12.5 Pulmonary Veins

Four pulmonary veins (right superior, right inferior, left superior, left inferior)
Drain oxygenated blood from the lungs into the left atrium
Enter the left atrium at its four corners (forming the base of the heart)
No valves at the pulmonary vein-atrial junction
The smooth posterior wall of the left atrium is derived from the incorporated proximal pulmonary veins

12.6 Brachiocephalic Veins

Right brachiocephalic vein: Short (~2.5 cm); formed behind the right sternoclavicular joint
Left brachiocephalic vein: Long (~6 cm); crosses the midline horizontally behind the manubrium
Both drain: internal jugular vein + subclavian vein
They join to form the SVC at the right 1st costal cartilage level

13. FETAL CIRCULATION AND POSTNATAL CHANGES

Fetal Structure	Function	Postnatal Remnant
Foramen ovale	Right-to-left shunt at atrial level (IVC blood bypasses lungs)	Fossa ovalis (closed in most)
Ductus arteriosus	Shunt between pulmonary trunk and aortic arch (bypasses lungs)	Ligamentum arteriosum
Ductus venosus	Shunt bypassing hepatic circulation in umbilical vein	Ligamentum venosum
Umbilical arteries	Carry deoxygenated blood from fetus to placenta	Medial umbilical ligaments
Umbilical vein	Carries oxygenated blood from placenta to fetus	Ligamentum teres hepatis

At birth, with the first breath:

Pulmonary vascular resistance falls
Left atrial pressure rises, closing the foramen ovale
Increased oxygen tension causes contraction of the ductus arteriosus (closes within hours; anatomically within weeks)

14. LYMPHATICS OF THE HEART

Dense lymphatic network divided into: deep endocardial, middle myocardial, and superficial epicardial networks
Larger collecting vessels travel in the epicardium accompanying the aorta and pulmonary trunk
Drain to tracheobronchial lymph nodes and anterior mediastinal lymph nodes

15. PERICARDIAL RELATIONS AND IMPORTANT ANATOMICAL POINTS

Posterior relations of the heart: Esophagus (immediately behind the left atrium - basis for transesophageal echocardiography), descending aorta, azygos vein
Anterior relations: Sternum and costal cartilages (2nd-6th), thymus remnant
Inferior relations: Diaphragm (central tendon)
Superiorly: Great vessels (aorta, pulmonary trunk, SVC)

Key Clinical-Anatomical Points

Point	Significance
Apex beat (cardiac impulse)	Left 5th ICS, midclavicular line - formed by left ventricle
Cardiac tamponade	Blood in pericardial cavity compresses the heart; rigid fibrous pericardium prevents expansion
Sternal angle (angle of Louis)	Level T4/T5 - marks bifurcation of trachea, arch of aorta, SVC entering pericardium
Moderator band (septomarginal trabecula)	Carries right bundle branch; clinically important landmark in RV
Coarctation of aorta	Narrowing at aortic isthmus (just distal to left subclavian artery origin)
PFO	Patent foramen ovale - present in ~25% of adults; potential paradoxical embolism pathway

Summary Table: Four Chambers at a Glance

Feature	Right Atrium	Right Ventricle	Left Atrium	Left Ventricle
Inflow	SVC, IVC, coronary sinus	Tricuspid valve	4 pulmonary veins	Mitral valve
Outflow	Tricuspid valve	Pulmonary valve (infundibulum)	Mitral valve	Aortic valve (vestibule)
Wall texture	Pectinate muscles (anterior); smooth (posterior)	Trabeculae carneae (inflow), smooth (outflow)	Mostly smooth	Thick trabeculae carneae
Wall thickness	Thin	3-5 mm	Thin	8-12 mm
Septal feature	Fossa ovalis	Membranous + muscular IVS	Fossa ovalis (left side)	Membranous + muscular IVS
Papillary muscles	3 (ant., post., septal)	3	None (AV valve has subvalvular apparatus)	2 (ant., post.)

Sources:

Gray's Anatomy for Students (9780323934237), pp. 226-252
Color Atlas of Human Anatomy Vol. 2, Internal Organs (9783132424487), pp. 40-65
Goldman-Cecil Medicine International Edition (9780323930345)

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