The four valves of the heart are the tricuspid valve, the pulmonary valve, the mitral valve, and the aortic valve. Each one acts as a one-way gate, opening to let blood through and snapping shut to prevent it from flowing backward. Together, they keep blood moving in a single direction: from your body to your lungs, back through your heart, and out to your body again.
How the Four Valves Work Together
Your heart has four chambers: two upper chambers (atria) and two lower chambers (ventricles). The four valves sit at the exits of these chambers, and they open and close in a coordinated sequence with every heartbeat. Blood always flows in one loop, and each valve ensures it moves forward through the next stage of that loop.
The path goes like this: oxygen-poor blood returning from your body enters the right atrium, passes through the tricuspid valve into the right ventricle, then gets pumped through the pulmonary valve toward the lungs. In the lungs, blood picks up fresh oxygen. That oxygen-rich blood flows into the left atrium, passes through the mitral valve into the left ventricle, and finally gets pumped through the aortic valve out to the rest of your body.
The valves fall into two functional pairs. The tricuspid and mitral valves are called atrioventricular valves because they sit between an atrium and a ventricle. They open when the upper chambers squeeze and close when the lower chambers start to contract, preventing blood from washing back upward. The pulmonary and aortic valves are called semilunar valves because of their crescent-shaped flaps. They guard the exits of the ventricles and slam shut the moment the ventricles relax, so blood doesn’t slide back down into the heart.
Tricuspid Valve
The tricuspid valve sits between the right atrium and the right ventricle. It has three thin flaps (leaflets) that swing open to let oxygen-poor blood drop into the right ventricle, then close tightly to stop any backflow. It is the first valve blood encounters after returning from the body through the large veins.
Pulmonary Valve
The pulmonary valve guards the exit of the right ventricle. When the right ventricle contracts, this valve opens and blood is pushed into the pulmonary artery, which carries it to the lungs. Once the ventricle relaxes, the valve closes so blood doesn’t fall back into the heart. It has three small, cup-shaped flaps.
Mitral Valve
The mitral valve connects the left atrium to the left ventricle. Unlike the other three valves, which each have three flaps, the mitral valve has only two. For that reason it is sometimes called the bicuspid valve. Oxygen-rich blood arriving from the lungs passes through it on its way into the powerful left ventricle. Because the left side of the heart generates much higher pressure than the right, the mitral valve endures significant mechanical stress with every beat, which is one reason it is the valve most commonly affected by degenerative disease.
Aortic Valve
The aortic valve is the final gate. It opens when the left ventricle contracts, sending oxygen-rich blood into the aorta, the body’s largest artery, which branches out to supply every organ and tissue. It has three flaps and must withstand the highest pressures in the entire circulatory system. Some people are born with only two flaps instead of three, a common variation called a bicuspid aortic valve, which can work fine for decades but raises the long-term risk of narrowing or leaking.
What Heart Sounds Tell You
The familiar “lub-dub” you hear through a stethoscope is the sound of these valves closing. The first sound (“lub”) happens when the tricuspid and mitral valves shut at the start of a heartbeat, as the ventricles begin to squeeze. The second sound (“dub”) is the pulmonary and aortic valves snapping closed once the ventricles finish contracting and start to relax. When a valve doesn’t open or close properly, turbulent blood flow creates an extra whooshing noise known as a heart murmur.
Common Valve Problems
Valve disease generally falls into two categories. Stenosis means a valve’s opening has become too narrow, forcing the heart to work harder to push blood through. The flaps may have thickened or stiffened, often from calcium buildup over many years. Regurgitation (also called insufficiency or a “leaky valve”) means a valve doesn’t seal tightly, allowing blood to flow backward. Both problems make the heart less efficient and, over time, can weaken it.
A third condition, mitral valve prolapse, occurs when one or both flaps of the mitral valve bulge back into the left atrium during contraction. It is common and usually harmless, though in some cases the bulging flaps leak enough blood to require treatment.
Valve disease becomes more common with age. Globally in 2021, there were an estimated 13.3 million cases of calcific aortic valve disease and 15.5 million cases of degenerative mitral valve disease, according to data published in the Journal of the American Heart Association. Among people 70 and older, roughly 2 in every 100 had significant aortic valve calcification, and a similar proportion had degenerative mitral disease. Rheumatic heart disease, caused by untreated strep infections, remains the leading cause of valve damage in lower-income countries, affecting an estimated 54.8 million people worldwide.
How Damaged Valves Are Treated
Mild valve disease often needs nothing more than regular monitoring. When a valve deteriorates enough to cause symptoms like shortness of breath, chest pain, or fatigue, repair or replacement becomes necessary.
Surgeons can sometimes repair a valve by reshaping or reinforcing the existing flaps, which is preferred when possible because it preserves natural tissue. When repair isn’t an option, the valve is replaced with either a mechanical prosthesis or a biological one made from animal tissue. Mechanical valves are extremely durable (only about 2.3% of patients need a second operation within 12 years), but they require lifelong blood-thinning medication because the artificial surface promotes clotting. That blood thinner carries its own risks: in one large study, 3.7% of mechanical valve patients experienced a bleeding-related stroke within 12 years. Biological valves don’t require long-term blood thinners, but they wear out faster, with about 5.2% of patients needing reoperation in the same timeframe. The choice between the two depends largely on age and how well a person can manage daily blood-thinner therapy.
For patients who are too frail for open-heart surgery, less invasive catheter-based procedures can deliver a new valve through a blood vessel, most commonly for the aortic valve. Recovery is faster, and outcomes have improved dramatically over the past decade.