Heart valves act as one-way doors inside your heart, opening and closing with every heartbeat to keep blood flowing in the correct direction. Your heart has four of them, and together they ensure that blood moves forward through the heart’s chambers and out to your lungs and body without leaking backward. Without functioning valves, your heart would have to work dramatically harder to deliver oxygen-rich blood where it needs to go.
How Heart Valves Work
Each valve is made of thin but strong flaps of tissue called leaflets. These leaflets swing open when blood pressure pushes against them from the correct side, then snap shut when the pressure shifts, preventing backflow. The entire process is passive: no muscles control the leaflets directly. Instead, pressure differences between the heart’s chambers do all the work.
A single heartbeat involves a carefully timed sequence. When the heart’s lower chambers (ventricles) contract to pump blood out, two valves open to let blood flow into the arteries while the other two slam shut to prevent blood from sliding back into the upper chambers. When the ventricles relax, the pattern reverses: the arterial valves close to stop blood from falling back into the heart, and the chamber valves open so fresh blood can fill the ventricles for the next beat. This coordinated opening and closing happens roughly 100,000 times a day.
The Four Valves and Their Positions
Your heart has two types of valves in two different locations. The valves between the upper and lower chambers (atrioventricular valves) control blood entering the ventricles. The valves between the ventricles and the major arteries (semilunar valves) control blood leaving the heart.
- Tricuspid valve: Sits between the right atrium and right ventricle. It has three leaflets and allows oxygen-depleted blood returning from the body to enter the right ventricle.
- Pulmonary valve: Guards the exit from the right ventricle into the pulmonary artery, directing blood toward the lungs to pick up oxygen.
- Mitral valve: Sits between the left atrium and left ventricle. It has two leaflets and allows oxygen-rich blood from the lungs to fill the left ventricle.
- Aortic valve: Guards the exit from the left ventricle into the aorta, the body’s largest artery. Blood passing through this valve is on its way to every organ and tissue.
Blood follows a fixed loop: body → right atrium → tricuspid valve → right ventricle → pulmonary valve → lungs → left atrium → mitral valve → left ventricle → aortic valve → body. The valves enforce that sequence, preventing blood from cutting corners or reversing course.
What Keeps the Valves in Place
The mitral and tricuspid valves face enormous pressure every time the ventricles contract, which could easily force their leaflets to blow backward into the upper chambers. To prevent this, thin cords of tissue called chordae tendineae anchor the leaflet edges to small muscles on the ventricle walls (papillary muscles). These cords work like the cables on a parachute, holding the leaflets taut so they seal shut without flipping inside out. The papillary muscles tighten during each contraction to keep the cords at the right tension.
The aortic and pulmonary valves don’t need this anchoring system. Their leaflets are shaped like small cups that fill with blood when it tries to flow backward, pressing together to form a tight seal. Small pockets behind the leaflets, called sinuses, create tiny swirling currents of blood during each heartbeat that help the leaflets begin closing even before forward flow stops, making the seal almost instantaneous.
What Happens When Valves Fail
Valve problems generally fall into two categories: a valve that won’t open fully, or a valve that won’t close completely.
When a valve narrows (stenosis), blood has to squeeze through a smaller opening. This forces the heart to generate higher pressures to push the same volume of blood forward. In aortic stenosis, for example, calcium deposits gradually stiffen the leaflets over years, restricting how wide they can swing open. The heart muscle thickens in response to the extra workload, and over time this can lead to fatigue, shortness of breath, and chest pain.
When a valve leaks (regurgitation), some blood sloshes backward with every beat. The heart compensates by pumping a larger total volume to make up for what’s lost to backflow. Mitral valve prolapse, where one or both mitral leaflets bulge into the upper chamber during contraction, is one common cause. In up to 25% of cases, this prolapse eventually leads to significant leaking that may require surgical repair, though this typically develops gradually over many years.
Both types of valve dysfunction make the heart less efficient. It’s like a door that’s stuck partway closed or a door that won’t latch. Either way, the heart has to burn more energy to accomplish the same job, and that extra strain compounds over time.
How Common Valve Problems Are
Valve disease becomes increasingly common with age. A 2025 study from the American College of Cardiology screened 3,000 Americans between ages 65 and 85 and found that 8.2% had moderate or greater valve disease. When milder cases were included, the number jumped to 18.4%. Extrapolated nationally, that translates to at least 10.6 million Americans living with clinically significant valve disease, many of whom don’t know it.
Nearly 60% of people with significant valve disease are women. The prevalence is projected to grow by almost 4 million additional cases by 2060, driven largely by a 74% increase in the 80-to-85 age group as the population ages. Black individuals have roughly 20% lower rates of valve disease compared to White individuals after adjusting for age and sex, primarily because of lower rates of aortic valve disease.
Signs a Valve Isn’t Working Properly
Mild valve problems often produce no symptoms at all, which is why so many cases go undetected. As dysfunction worsens, common signs include shortness of breath during activity or when lying flat, unusual fatigue, swelling in the ankles or feet, dizziness, and a fluttering or irregular heartbeat. A heart murmur, an extra or unusual sound heard through a stethoscope, is often the first clue that a valve isn’t opening or closing correctly.
Valve disease is typically identified through echocardiography, an ultrasound of the heart that shows the valves in motion and measures how well blood flows through them. Doctors assess severity by looking at several factors together: how the valve looks structurally, how fast blood moves through it, how much blood leaks backward, and whether the heart’s chambers have started to enlarge or weaken in response.