Heart function
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"cardiac output"
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heart function cardiac cycle cardiac output American Heart Association
The heart functions as a muscular pump that maintains blood circulation.
- The right side receives oxygen-poor blood from the body and pumps it to the lungs for oxygenation.
- The left side receives oxygen-rich blood from the lungs and pumps it through the aorta to the rest of the body.
- Its rhythmic contraction and relaxation is the cardiac cycle:
- Diastole: chambers relax and fill with blood.
- Systole: ventricles contract and eject blood.
- Cardiac output is the blood pumped each minute:
[
\text{Cardiac output} = \text{heart rate} \times \text{stroke volume}
]
At rest, it is roughly 5 L/min in a typical adult, but rises substantially during exercise.
The heart also helps maintain blood pressure and ensures oxygen and nutrients reach tissues while removing carbon dioxide and metabolic waste.
Explain the four chambers and heart valves
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labeled diagram of four chambers of human heart and four valves blood flow
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"heart valves" AND anatomy
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heart chambers valves blood flow anatomy NIH
The heart has four chambers: two upper receiving chambers called atria and two lower pumping chambers called ventricles.
The four chambers
| Chamber | Main role | Blood it handles |
|---|---|---|
| Right atrium | Receives blood returning from the body through the superior and inferior vena cava | Oxygen-poor blood |
| Right ventricle | Pumps this blood to the lungs through the pulmonary artery | Oxygen-poor blood |
| Left atrium | Receives newly oxygenated blood from the lungs through the pulmonary veins | Oxygen-rich blood |
| Left ventricle | Pumps oxygen-rich blood through the aorta to the whole body | Oxygen-rich blood |
The left ventricle has the thickest muscular wall because it must generate enough pressure to send blood throughout the body. The right ventricle pumps only to the nearby lungs, so it works against lower pressure.
The four heart valves
Heart valves act like one-way doors. They open when pressure behind them rises and close when pressure would otherwise push blood backward. The four valves maintain one-directional blood flow, as described in Robbins, Cotran & Kumar Pathologic Basis of Disease, section “Valves,” lines 561-569.
-
Tricuspid valve
- Between the right atrium and right ventricle
- Opens to allow blood into the right ventricle.
- Closes when the right ventricle contracts, preventing backflow into the right atrium.
-
Pulmonary valve
- Between the right ventricle and the pulmonary artery
- Opens when the right ventricle pumps blood toward the lungs.
- Closes afterward to prevent blood returning to the ventricle.
-
Mitral valve, also called the bicuspid valve
- Between the left atrium and left ventricle
- Opens to allow oxygen-rich blood into the left ventricle.
- Closes during ventricular contraction to prevent backflow into the left atrium.
-
Aortic valve
- Between the left ventricle and the aorta
- Opens when the left ventricle contracts and sends blood to the body.
- Closes so blood cannot fall back from the aorta into the ventricle.
Blood-flow pathway
Body → right atrium → tricuspid valve → right ventricle → pulmonary valve → lungs → left atrium → mitral valve → left ventricle → aortic valve → body
The NHLBI heart anatomy overview and its blood-flow explanation illustrate this pathway and describe how valve leaflets prevent backward flow.
Compare the mitral and tricuspid valves
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"mitral valve" AND "tricuspid valve"
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mitral tricuspid valve anatomy comparison NIH
Both are atrioventricular (AV) valves. They lie between an atrium and a ventricle, open during ventricular filling, and close during ventricular contraction to prevent backflow into the atria.
| Feature | Mitral valve | Tricuspid valve |
|---|---|---|
| Location | Between left atrium and left ventricle | Between right atrium and right ventricle |
| Blood | Oxygen-rich blood returning from lungs | Oxygen-poor blood returning from body |
| Number of leaflets | 2 leaflets, so also called bicuspid valve | 3 leaflets |
| Leaflets | Anterior and posterior | Anterior, posterior, and septal |
| Pressure handled | High pressure, because the left ventricle pumps to the whole body | Lower pressure, because the right ventricle pumps only to the lungs |
| Papillary muscles | Usually 2: anterolateral and posteromedial | Usually 3, corresponding broadly to its three leaflets |
| Common disease pattern | Mitral stenosis and mitral regurgitation are relatively common clinically | Tricuspid regurgitation is often secondary to enlargement of the right ventricle or pulmonary hypertension |
Similar structure and action
Both valves have:
- A fibrous ring called the annulus
- Thin leaflets
- Chordae tendineae, fibrous cords attached to the leaflets
- Papillary muscles, which tighten the chordae during systole
The chordae and papillary muscles prevent the valve leaflets from being pushed backward into the atria when the ventricles contract.
Simple memory aid
- Mitral = Left = 2 leaflets
- Tricuspid = Right = 3 leaflets
The NHLBI blood-flow overview identifies the mitral valve between the left atrium and ventricle, and the tricuspid valve between the right atrium and ventricle.
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