Mitral stenosis is a condition where the mitral valve in your heart becomes narrowed, restricting blood flow from the upper left chamber (left atrium) to the lower left chamber (left ventricle). A normal mitral valve opens wide enough to let blood pass freely, but when the valve opening shrinks below 2 square centimeters, it starts creating a bottleneck that forces your heart to work harder and raises pressure in your lungs.
How Mitral Stenosis Affects Your Heart
Your mitral valve sits between the two left chambers of the heart. With each heartbeat, it opens to let oxygen-rich blood flow down from the left atrium into the left ventricle, which then pumps it out to the rest of your body. When the valve stiffens or narrows, blood can’t move through as easily, and pressure builds up behind the obstruction.
That backup of pressure is what drives most of the problems. Normal pressure in the left ventricle during filling is about 5 mmHg. In severe mitral stenosis, the pressure difference across the valve can reach 20 mmHg, pushing left atrial pressure up to around 25 mmHg. That elevated pressure doesn’t stay contained in the left atrium. It transmits backward into the blood vessels of the lungs, leading to pulmonary hypertension, which is the root cause of many symptoms.
What Causes the Valve to Narrow
Rheumatic fever is by far the most common cause worldwide. This inflammatory condition, triggered by untreated strep throat, can damage the mitral valve leaflets over time, causing them to thicken, scar, and fuse together. The damage often takes years or even decades to become severe enough to cause symptoms, which is why mitral stenosis frequently shows up in adults who had rheumatic fever as children.
In countries where strep infections are treated early with antibiotics, rheumatic mitral stenosis has become less common but hasn’t disappeared. Other, rarer causes include heavy calcification of the valve ring (more common in older adults), congenital heart defects present from birth, and certain autoimmune conditions.
Symptoms and How They Progress
Mitral stenosis often develops silently. You can have a narrowed valve for years before noticing anything, because the body compensates well in the early stages. Symptoms typically appear when the valve area drops below 1.5 square centimeters or when something increases your heart rate, like exercise, fever, or pregnancy.
The most common symptom is shortness of breath, especially during physical activity or when lying flat. This happens because elevated pressure in the lung vessels causes fluid to leak into lung tissue. As the condition worsens, you may notice shortness of breath even at rest. Other symptoms include fatigue, a persistent cough (sometimes with blood-tinged sputum), heart palpitations, and swelling in the legs or abdomen. Coughing up blood, while alarming, results from the high pressure in lung blood vessels and is a recognized feature of more advanced disease.
The Link to Atrial Fibrillation and Stroke
The chronically elevated pressure in the left atrium causes it to stretch and enlarge over time. An enlarged atrium is prone to developing atrial fibrillation, an irregular heart rhythm where the upper chambers quiver instead of beating effectively. This is one of the most serious complications of mitral stenosis, and it creates a dangerous chain reaction: when blood pools in an irregularly beating atrium, clots can form, travel to the brain, and cause a stroke.
The numbers are sobering. In developing countries, mitral stenosis combined with atrial fibrillation accounts for roughly 80% of strokes in people with rheumatic heart disease. Overall, clots from mitral stenosis are responsible for about 10% of all ischemic strokes and half of all strokes caused by heart-related blood clots. The stroke risk runs about 4.5 per 100 patient-years, comparable to the risk seen in other forms of atrial fibrillation. Blood thinners significantly reduce this risk, bringing it down to between 0.4 and 4 per 100 patient-years depending on the study.
How Mitral Stenosis Is Diagnosed
A doctor may first suspect mitral stenosis after hearing a characteristic murmur through a stethoscope, but an echocardiogram (heart ultrasound) is the standard tool for confirming the diagnosis and measuring severity. The echo shows the valve’s structure, how well it opens, and how much pressure is building up across it.
Severity is classified based on the pressure difference across the valve, measured as the mean gradient. A gradient below 5 mmHg is considered mild, 5 to 10 mmHg is moderate, and above 10 mmHg is severe (these measurements are most accurate when the heart rate is between 60 and 80 beats per minute). The echocardiogram also evaluates how stiff, thickened, or calcified the valve leaflets have become, which is critical for deciding what type of treatment will work best.
Treatment Options
Mild mitral stenosis often needs no intervention beyond monitoring. If symptoms develop, medications can help manage them by slowing the heart rate, which gives the blood more time to pass through the narrowed valve during each heartbeat. Diuretics can reduce fluid buildup in the lungs. If atrial fibrillation develops, blood thinners become essential to prevent clots.
When symptoms are significant and the valve is still relatively pliable, a procedure called percutaneous balloon valvuloplasty is typically the first-line treatment. A catheter with a balloon at its tip is threaded through a vein into the heart, positioned in the narrowed valve, and inflated to widen the opening. This works best for valves that haven’t become heavily calcified or scarred, and when there’s no significant leaking (regurgitation) of the valve or blood clot in the left atrium. It’s also a strong option for patients who are older or at high risk for open-heart surgery.
Before the procedure, doctors use a detailed scoring system to assess the valve’s condition, evaluating four characteristics: how mobile the leaflets are, how thick they’ve become, how much calcium has deposited, and how damaged the supporting structures beneath the valve are. Valves with low scores, meaning they’re still relatively flexible and minimally calcified, tend to respond well to balloon treatment. Heavily scarred or calcified valves are poor candidates.
Valve Replacement Surgery
When the valve is too damaged for balloon treatment, surgical replacement becomes necessary. There are two main types of replacement valves, each with trade-offs. Mechanical valves are extremely durable and can last a lifetime, but they require you to take blood-thinning medication indefinitely, along with regular blood monitoring and some dietary restrictions. Bioprosthetic valves, made from animal tissue, don’t require long-term blood thinners, which makes daily life simpler. The downside is that they gradually wear out over time through a process of calcium buildup and tissue breakdown, eventually needing replacement. The choice between the two depends on your age, lifestyle, and tolerance for lifelong anticoagulation.
Mitral Stenosis During Pregnancy
Pregnancy poses a unique challenge for women with mitral stenosis. The normal cardiovascular changes of pregnancy, including increased blood volume, faster heart rate, and higher cardiac output, all push more blood through a valve that can’t accommodate it. The result is a significant rise in complications.
Women with moderate to severe stenosis face higher rates of pulmonary edema (fluid flooding the lungs), dangerous heart rhythms, and blood clots. Having a valve area below 2.0 square centimeters, a history of prior heart failure or arrhythmia, or reduced heart pumping function all independently predict cardiac complications. One study found that a history of prior cardiac events increased the odds of complications nearly sevenfold. Fetal risks are also elevated, including preterm delivery, low birth weight, restricted growth, and in severe cases, fetal or neonatal death.
For women with known moderate to severe mitral stenosis, the ideal approach is evaluation and treatment before becoming pregnant. If the valve is suitable, balloon valvuloplasty can be performed before conception to reduce risk. During pregnancy, the primary strategy is keeping the heart rate slow enough to allow adequate blood flow through the narrowed valve. Heart rate-lowering medications are the cornerstone of management, and diuretics may be used cautiously when fluid builds up, though doctors try to avoid reducing blood flow to the placenta. During labor, the goals are controlling heart rate and managing fluid balance carefully, often with epidural pain relief to prevent the spikes in heart rate that come with pain.