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Describe the structure, relations, and blood supply of the heart.

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Heart structure (gross anatomy)
  • The heart is a hollow muscular organ in the middle mediastinum, enclosed by the pericardium.
  • It has 4 chambers:
    1. Right atrium (RA): receives deoxygenated blood from SVC, IVC, and coronary sinus.
    2. Right ventricle (RV): pumps blood to pulmonary trunk.
    3. Left atrium (LA): receives oxygenated blood from 4 pulmonary veins.
    4. Left ventricle (LV): pumps blood to aorta; has the thickest wall.
  • Apex: inferolateral tip, mainly LV, usually at left 5th intercostal space midclavicular line.
  • Base: posterior aspect, mainly LA.
  • Surfaces:
    • Sternocostal (anterior): mainly RV
    • Diaphragmatic (inferior): mainly LV + partly RV
    • Right pulmonary: RA
    • Left pulmonary: LV
  • Cardiac skeleton: dense fibrous rings around valves; supports valves and electrically insulates atria from ventricles (except AV bundle).
Internal features and valves
  • Right atrium: smooth sinus venarum posteriorly, pectinate muscles anteriorly, fossa ovalis on septum.
  • Right ventricle: trabeculae carneae, papillary muscles, moderator band.
  • Left atrium: mostly smooth; pectinate muscles mainly in left auricle.
  • Left ventricle: thick myocardium, fine trabeculae, two large papillary muscles.
  • Valves:
    • Tricuspid: RA to RV
    • Pulmonary: RV to pulmonary trunk
    • Mitral (bicuspid): LA to LV
    • Aortic: LV to aorta
  • AV valve leaflets are anchored by chordae tendineae to papillary muscles to prevent prolapse during systole.

Relations of the heart

Pericardial relations
  • Heart lies within fibrous and serous pericardium.
  • Fibrous pericardium is attached inferiorly to central tendon of diaphragm, anteriorly to sternum (sternopericardial ligaments), and blends superiorly with great vessel adventitia.
Anterior
  • Sternum, costal cartilages, anterior mediastinal pleura/lungs (with pleural recesses).
Posterior
  • Esophagus, descending thoracic aorta, thoracic vertebral bodies (via posterior mediastinum).
  • Clinically relevant: enlarged LA can compress esophagus.
Inferior
  • Diaphragm (central tendon), left lobe of liver indirectly below diaphragm.
Lateral
  • Lungs and mediastinal pleura.
  • Phrenic nerves and pericardiacophrenic vessels run on each side of fibrous pericardium (between pleura and pericardium).
Great vessel relations
  • Pulmonary trunk is anterior/left of ascending aorta initially.
  • SVC enters RA superiorly; IVC enters inferiorly.
  • Pulmonary veins enter posterior LA.

Blood supply of the heart

1) Arterial supply (coronary arteries)

Coronary arteries arise from ascending aortic sinuses just above aortic valve.
Right coronary artery (RCA)
  • Origin: right aortic sinus
  • Course: right AV groove
  • Major branches:
    • SA nodal branch (commonly from RCA)
    • Right marginal artery
    • AV nodal branch (usually from RCA)
    • Posterior interventricular artery (PDA) in most people
  • Supplies: RA, most RV, inferior/posterior LV (variable), posterior 1/3 of IV septum, often SA and AV nodes.
Left coronary artery (LCA, left main)
  • Origin: left aortic sinus
  • Short trunk divides into:
    • LAD (anterior interventricular artery): anterior IV groove; gives diagonal and septal branches.
    • LCx (circumflex artery): left AV groove; gives obtuse marginal branches.
  • Supplies: most LA and LV, part of RV, anterior 2/3 of IV septum, AV bundle and bundle branches.

2) Coronary dominance

Defined by which artery gives rise to PDA:
  • Right-dominant (~70%): PDA from RCA
  • Left-dominant (~10%): PDA from LCx
  • Co-dominant (~20%): contribution from both
Dominance affects infarct territory and conduction ischemia risk.

3) Venous drainage

Most venous blood drains to coronary sinus → RA. Major tributaries:
  • Great cardiac vein (with LAD)
  • Middle cardiac vein (with PDA)
  • Small cardiac vein (with RCA/right marginal) Also:
  • Anterior cardiac veins (RV) drain directly to RA
  • Thebesian veins (smallest cardiac veins) drain directly into chambers

4) Lymphatic drainage

Subepicardial lymphatics follow coronary arteries to tracheobronchial nodes, then to mediastinal trunks.

Quick functional flow

Systemic veins → RA → tricuspid → RV → pulmonary valve → lungs → pulmonary veins → LA → mitral → LV → aortic valve → systemic arteries.
If you want, I can add a labeled schematic-style summary table of chamber walls, valve positions, and coronary territories for quick revision.
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