---
title: Heart valves
description: Where the four heart valves are, how they are built and why they open and close at the right moment.
type: anatomy
aliases:
  - cardiac valves
  - valves of the heart
  - atrioventricular valves
  - semilunar valves
sources:
  - tier: textbook
    title: Anatomy and Physiology 2e (OpenStax), Chapter 19
    year: 2022
    isbn: 9781711494067
    url: https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy
  - tier: reference
    org: statpearls
    title: Anatomy, Thorax, Mitral Valve
    year: 2023
    url: https://www.ncbi.nlm.nih.gov/books/NBK549884/
  - tier: reference
    org: statpearls
    title: Anatomy, Thorax, Aortic Valve
    year: 2023
    url: https://www.ncbi.nlm.nih.gov/books/NBK559384/
  - tier: reference
    org: statpearls
    title: Anatomy, Thorax, Heart Pulmonic Valve
    year: 2023
    url: https://www.ncbi.nlm.nih.gov/books/NBK547706/
sources_checked: 2026-10-11
review: null
---

The heart has four valves, and together they make sure that blood flows through the heart in one direction only.<Cite n={1} /> Two valves sit between the atria and the ventricles: the tricuspid valve on the right and the mitral valve on the left.<Cite n={[1, 4]} /> The other two sit where the ventricles open into the large arteries: the pulmonary valve and the aortic valve.<Cite n={[1, 4]} />

<Diagram name="heart-valves">
  <p slot="diastole">The ventricles relax. The pressure inside them is lower than in the atria, so blood pushes open the tricuspid and mitral valves and fills the ventricles, while the pulmonary and aortic valves are closed.<Cite n={1} /> At the very start of diastole, while the pressure in the ventricles is still higher than in the atria, all four valves are closed.<Cite n={1} /></p>
  <p slot="systole">The ventricles contract. The pressure inside them is higher than in the atria, so the tricuspid and mitral valves are closed. Once it rises above the pressure in the pulmonary trunk and the aorta, blood pushes open the pulmonary and aortic valves.<Cite n={1} /> At the very start of systole, while the pressure is still rising, all four valves are closed.<Cite n={1} /></p>
</Diagram>

## How it is built

<Patient>

The **<Structure id="tricuspid-valve">tricuspid valve</Structure>** lies between the right atrium and the right ventricle.<Cite n={1} /> It usually has three flaps.<Cite n={1} />

The **<Structure id="pulmonary-valve">pulmonary valve</Structure>** sits where the pulmonary trunk leaves the right ventricle.<Cite n={[1, 4]} /> It is made of three small flaps.<Cite n={[1, 4]} />

The **<Structure id="mitral-valve">mitral valve</Structure>** lies between the left atrium and the left ventricle.<Cite n={[1, 2]} /> It is also called the bicuspid valve, because it has two flaps.<Cite n={[1, 2]} />

The **<Structure id="aortic-valve">aortic valve</Structure>** lies between the left ventricle and the aorta.<Cite n={3} /> It usually has three flaps.<Cite n={[1, 3]} />

The flaps of the tricuspid and mitral valves are tied by thin cords (the chordae tendineae) to the papillary muscles on the wall of the ventricle.<Cite n={[1, 2]} /> The pulmonary and aortic valves have no such cords or muscles.<Cite n={1} /> The valves are attached to a firm framework of dense connective tissue called the cardiac skeleton.<Cite n={1} />

</Patient>

<Student>

The valves fall into two groups: the atrioventricular valves (mitral and tricuspid) and the semilunar valves (aortic and pulmonary, or pulmonic).<Cite n={4} /> The aortic valve is called semilunar because of the shape of its cusps.<Cite n={3} />

The mitral valve has an anterior and a posterior leaflet.<Cite n={2} /> The mitral annulus is a fibrous ovoid ring around the mitral opening.<Cite n={2} /> The chordae arise mainly from two papillary muscles, the anterolateral and the posteromedial, and with every ventricular contraction they stop the leaflets from prolapsing into the atrium.<Cite n={2} />

The aortic cusps and the sinuses behind them are named after the coronary arteries that arise from the sinuses: left coronary, right coronary and non-coronary.<Cite n={3} /> The sinuses ensure that the cusps do not occlude the coronary ostia during systole.<Cite n={3} /> The pulmonary valve has anterior, left and right cusps.<Cite n={4} /> It is separated from the tricuspid valve by a muscular fold, the supraventricular crest (ventriculoinfundibular fold).<Cite n={4} />

</Student>

<HeartModel highlight={['tricuspid-valve', 'pulmonary-valve', 'mitral-valve', 'aortic-valve']} />

## How it works

<Patient>

The valves open and close because of the difference in pressure on either side of them: the flow of blood pushes them.<Cite n={1} /> Blood always moves from where the pressure is higher to where it is lower.<Cite n={1} />

While the ventricles are relaxed, the pressure inside them is lower than in the atria, so the tricuspid and mitral valves are open and blood fills the ventricles, while the pulmonary and aortic valves are closed.<Cite n={1} /> When the ventricles start to contract, blood pushes back towards the atria and snaps the tricuspid and mitral valves shut.<Cite n={1} /> At the same time the papillary muscles contract and pull the cords tight, so the flaps cannot be pushed back into the atria.<Cite n={[1, 2]} /> When the pressure in the ventricles rises above the pressure in the pulmonary trunk and the aorta, blood pushes open the pulmonary and aortic valves and leaves the heart.<Cite n={[1, 3]} />

When the ventricles relax and their pressure falls, blood from the aorta and the pulmonary trunk fills the cusps of the semilunar valves and closes them.<Cite n={[1, 3]} /> Then the pressure in the ventricles drops below the pressure in the atria, the tricuspid and mitral valves open again, and the cycle repeats.<Cite n={1} /> The phases are described in more detail in the article ["The cardiac cycle"](../cardiac-cycle/).

You can hear the valves closing through a stethoscope.<Cite n={1} /> The first heart sound comes from the tricuspid and mitral valves closing as the ventricles contract.<Cite n={1} /> The second heart sound comes from the aortic and pulmonary valves closing as the ventricles relax.<Cite n={[1, 4]} />

</Patient>

<Student>

The aortic valve opens when left ventricular pressure exceeds aortic pressure, and closes when left ventricular pressure falls below that in the ascending aorta.<Cite n={3} /> The pulmonary valve opens in systole and closes in diastole, allowing sufficient filling of the right ventricle.<Cite n={4} /> The mitral valve prevents backflow of blood from the left ventricle into the left atrium during systole, and during diastole allows blood to flow from the left atrium into the left ventricle.<Cite n={2} />

Between closure of the atrioventricular valves and opening of the semilunar valves comes the phase of isovolumic contraction: all valves are closed, ventricular pressure rises and the volume of blood in the ventricles stays constant.<Cite n={1} /> A similar phase, isovolumic relaxation, follows closure of the semilunar valves until the atrioventricular valves open; the volume of blood in the ventricles does not change during it either.<Cite n={1} />

S1 is the sound of the atrioventricular valves closing during ventricular contraction; S2 is the sound of the semilunar valves closing during ventricular diastole.<Cite n={1} /> S2 has an aortic (A) and a pulmonary (P) component.<Cite n={4} />

</Student>

## In disease

A valve can become narrowed and obstruct forward flow (stenosis), or fail to close fully so that some blood leaks backwards (regurgitation, also called insufficiency).<Cite n={[2, 3]} /> Narrowing of the aortic valve has its own article: [aortic stenosis](../../disease/aortic-stenosis/).<Cite n={3} />

<Quiz />