The AV valves, short for atrioventricular valves, are the two one-way gates inside your heart that separate the upper chambers (atria) from the lower chambers (ventricles). Their job is straightforward: let blood flow downward from atrium to ventricle, then snap shut to prevent it from leaking back up. Your heart has two of them, one on each side, and together they’re essential for keeping blood moving in one direction.
The Two AV Valves and Where They Sit
Your heart’s right AV valve is called the tricuspid valve. It sits between the right atrium and the right ventricle and has three thin, strong flaps of tissue called leaflets. These three leaflets are named for their positions: anterior, posterior, and septal.
The left AV valve is the mitral valve, sometimes called the bicuspid valve because it has two leaflets instead of three. It sits between the left atrium and the left ventricle. Of the two, the mitral valve handles higher pressures because the left side of the heart pumps blood out to the entire body, while the right side only sends blood to the lungs.
A healthy mitral valve opening measures about 4 to 6 square centimeters. The tricuspid valve is similar in size, averaging roughly 4.8 square centimeters in adults. These openings are wide enough to let blood pass freely when the valve is open, yet small enough that the leaflets can seal completely when they close.
How AV Valves Open and Close
AV valves are passive structures. They don’t have muscles of their own. Instead, they respond to pressure differences between the chambers above and below them. When the ventricle relaxes after a heartbeat, pressure inside it drops below the pressure in the atrium above. That pressure difference pushes the valve leaflets open, and blood flows down to fill the ventricle.
Once the ventricle begins to contract, pressure inside it rises quickly. The moment ventricular pressure exceeds atrial pressure, the leaflets are forced upward and shut. This is where an important support system kicks in. Each leaflet is tethered to small muscles on the ventricle wall by thin, cord-like fibers called chordae tendineae (sometimes described as “heart strings”). When the ventricle contracts, these muscles contract at the same time, pulling the cords tight so the leaflets don’t flip inside out or bulge back into the atrium. Without that tethering, the force of contraction would push the leaflets the wrong way, and blood would leak backward.
The Sound Your AV Valves Make
When a doctor listens to your heart with a stethoscope, the first sound they hear with each beat (the “lub” in “lub-dub”) is produced by your AV valves closing. The mitral valve actually shuts about 20 to 30 milliseconds before the tricuspid valve, which can sometimes create a subtle split in that first sound. The vibrations happen because the entire valve system, including the leaflets, cords, and surrounding muscle, stretches to its elastic limit and then rebounds as the blood column is abruptly stopped. That snap of deceleration is what generates the audible sound on the chest wall.
What Goes Wrong: Regurgitation and Stenosis
AV valve problems generally fall into two categories. In regurgitation (also called insufficiency or backflow), the valve doesn’t seal tightly, so blood leaks backward into the atrium with every heartbeat. This forces the heart to work harder because some of the blood it just pumped ends up going the wrong direction. Regurgitation can happen when the leaflets are the wrong size or shape, or when the valve opening has stretched. The most common cause on the left side is mitral valve prolapse, where one or both leaflets sag and flop back into the atrium during contraction.
In stenosis, the valve opening becomes too narrow. The leaflets may be stiff, scarred, or fused together, making it difficult for blood to pass through. The heart compensates by pumping harder, but over time this extra workload can weaken the muscle. Stenosis can be present from birth or develop later in life from conditions like rheumatic fever or calcium buildup on the leaflets.
Mitral Valve Prolapse: The Most Common AV Valve Problem
Mitral valve prolapse is worth singling out because it’s extremely common. Many people with it have no symptoms at all and only discover it during a routine exam when a doctor hears a distinctive mid-systolic “click” followed by a murmur. That click is the sound of the leaflet billowing back further than it should.
When symptoms do occur, they can include palpitations, fatigue, exercise intolerance, chest discomfort that doesn’t feel like a typical heart attack, and occasional dizziness or lightheadedness. Some people also experience anxiety, mood changes, or episodes of fainting, likely related to how the condition affects the body’s autonomic nervous system. The diagnosis is confirmed with an echocardiogram (an ultrasound of the heart), which can show exactly how far the leaflet displaces and how thick it has become. A displacement of more than 2 millimeters above the valve ring is the diagnostic threshold.
How AV Valve Problems Are Monitored and Treated
For mild valve problems, monitoring is often all that’s needed. Serial echocardiograms let doctors track whether the leak or narrowing is getting worse and whether the heart’s pumping function is holding steady. This is especially important in mitral regurgitation, where the heart can compensate for a long time before symptoms appear, but waiting too long to intervene can lead to irreversible damage to the heart muscle.
When the problem becomes severe, the valve can be surgically repaired or replaced. Repair is generally preferred because it preserves the patient’s own tissue and avoids the lifelong blood-thinning medication that mechanical replacement valves require. For patients who are too high-risk for open heart surgery, a less invasive option called transcatheter edge-to-edge repair is available. In this procedure, a small clip is delivered through a blood vessel (no chest incision) and used to pinch the leaking leaflets together, reducing the backflow. Clinical trials have shown this approach reduces hospital stays for heart failure and improves survival compared to medication alone in patients with severe mitral regurgitation who aren’t good candidates for surgery. About 20% of patients do experience a notable drop in heart pumping strength afterward, so careful patient selection matters.
Tricuspid valve disease has historically received less attention, partly because right-sided heart pressures are lower and symptoms develop more slowly. But treatment options for the tricuspid valve are expanding, with newer catheter-based approaches being adapted from techniques originally developed for the mitral valve.