Myxomatous degeneration is a gradual, non-inflammatory breakdown of connective tissue in which the normal structural fibers weaken and get replaced by a loose, gel-like substance. It most commonly affects the heart valves, particularly the mitral valve, and is the underlying cause of mitral valve prolapse, a condition found in roughly 2.5% of the general population. While many people with myxomatous changes never develop symptoms, the condition can progress over years to cause significant valve leakage and, in some cases, require surgery.
What Happens Inside the Tissue
Healthy connective tissue gets its strength from tightly organized collagen and elastic fibers. In myxomatous degeneration, those fibers fragment and break apart while a sugary, gel-like substance called glycosaminoglycan accumulates in the spaces between cells. Under a microscope, the affected tissue looks swollen and spongy, with cyst-like spaces where dense, organized collagen used to be. The elastic fibers appear disrupted, granular, and clumped together rather than forming their normal springy network.
The process is driven by an imbalance between how the body builds and breaks down its structural scaffolding. Enzymes that digest connective tissue become overactive, chewing through collagen faster than cells can replace it. The result is tissue that’s progressively thinner, stretchier, and weaker than it should be. In a heart valve, this means leaflets that bulge and flop instead of snapping shut cleanly.
Why It Happens
Myxomatous degeneration often runs in families. Researchers have identified several chromosome regions linked to inherited forms of mitral valve prolapse, including locations on chromosomes 16, 11, and the X chromosome. In many people, though, the condition appears without a clear family history and is considered sporadic.
The strongest genetic connections involve inherited connective tissue disorders. Marfan syndrome, caused by mutations in a protein called fibrillin-1, is one of the most well-known associations. People with Ehlers-Danlos syndrome, osteogenesis imperfecta, and a related condition called MASS syndrome (which combines valve prolapse, aortic root widening, skeletal changes, and skin changes) also have significantly higher rates of myxomatous valve disease. In these conditions, the genes responsible for building connective tissue fibers are defective from the start, which either directly weakens valve structure or alters the way the heart muscle contracts, placing extra mechanical stress on the valves and triggering degeneration over time.
Where It Shows Up in the Body
The mitral valve is by far the most common site. This valve sits between the upper and lower left chambers of the heart, and its two leaflets open and close with every heartbeat. When myxomatous changes make the leaflets floppy and oversized, they billow backward into the upper chamber instead of closing flat. This is mitral valve prolapse.
The aortic valve can also be affected, though this is considerably rarer. Myxomatous changes in the aortic valve weaken its three leaflets, sometimes causing them to tear away from their attachment points. This leads to aortic regurgitation, where blood leaks backward into the heart after each beat. Cases have been reported in patients as young as their late thirties.
Outside the heart, myxomatous tissue changes appear in several other settings. In Carney complex, a rare genetic syndrome, myxomas (benign tumors made of the same gel-like myxoid tissue) can develop in the skin, particularly on the eyelids, ear canals, and nipples. Breast tissue can develop multiple myxoid growths bilaterally, a pattern sometimes called breast myxomatosis. Even bone can be involved, with unusual tumors containing a mix of myxoid material, cartilage, and bone elements.
Symptoms and How They Progress
Most people with myxomatous valve degeneration have no symptoms at all, especially early on. The condition is frequently discovered incidentally during a routine physical exam when a doctor hears a clicking sound or heart murmur, or during an echocardiogram ordered for another reason.
When symptoms do develop, they typically reflect the amount of blood leaking backward through the affected valve. Common complaints include a racing or irregular heartbeat, dizziness, fatigue, and shortness of breath during exercise or while lying flat. These symptoms tend to appear gradually over years or even decades as the valve leak worsens. The progression varies enormously from person to person. Some people remain stable for their entire lives, while others develop significant regurgitation that strains the heart.
Complications to Watch For
The most serious risk of myxomatous valve disease is rupture of the chordae tendineae, the thin cord-like structures that tether the valve leaflets to the heart muscle below. Myxomatous changes don’t just affect the leaflets; they weaken these cords too. Studies show that myxomatous chordae fail at roughly half the force required to break normal ones. When a chord snaps, the valve leaflet it was holding flails freely, and blood rushes backward with each heartbeat. This can cause sudden, severe regurgitation.
Chordal rupture is the single most common cause of acute mitral regurgitation in people with valve prolapse. Myxomatous degeneration and mitral valve prolapse together account for more than half of all chordal rupture cases. The consequences range widely. Some people develop acute heart failure with dramatic shortness of breath and fluid buildup. Others tolerate the rupture surprisingly well, and it’s occasionally found only at autopsy. The outcome depends on how many chords break, how much regurgitation results, and how well the heart compensates.
Over the long term, chronic valve leakage from any cause forces the heart to pump harder and can lead to enlargement of the heart chambers, irregular heart rhythms (particularly atrial fibrillation), and eventually heart failure if left untreated.
How It’s Diagnosed
Echocardiography is the primary tool. Both standard transthoracic echocardiograms (ultrasound through the chest wall) and transesophageal echocardiograms (ultrasound from a probe in the esophagus, closer to the heart) can identify the hallmark finding: valve leaflets that rise up and billow into the upper heart chamber instead of closing flush. The exam also evaluates the leaflets themselves, the valve ring, the chordae, and the muscles that anchor them, along with measuring how much blood is leaking backward.
The thickened, redundant leaflets characteristic of myxomatous disease are often visually distinct from valves damaged by other causes like infection or rheumatic disease. Combined with the clinical picture, echocardiography is usually sufficient to confirm the diagnosis without further testing.
Treatment and Surgical Options
People with mild myxomatous valve disease and no significant regurgitation generally need only periodic monitoring with echocardiograms to track any changes. Medications can help manage symptoms like irregular heartbeats or fluid retention when they develop, but no drug reverses the underlying tissue changes.
When regurgitation becomes severe, surgery is the definitive treatment. Current guidelines from both American and European cardiology societies are clear: valve repair is preferred over valve replacement whenever a durable repair is technically feasible. This recommendation is especially strong for degenerative (myxomatous) disease, where repair techniques have excellent long-term track records.
The outcomes data supports this preference convincingly. In patients with degenerative mitral regurgitation, repair is associated with better long-term survival, shorter hospital stays, less blood loss, fewer transfusions, and lower rates of stroke compared to replacement. Replacement patients had a stroke rate of 3.7% versus just 0.4% for repair in one large matched analysis. While repair does carry a somewhat higher chance of needing a second operation down the line (about 4.3% versus 2.1%), the combined risk of death or reoperation doesn’t significantly differ between the two approaches, and the survival advantage of repair persists over the long term.
Surgery is recommended when the heart starts showing signs of strain, specifically when the pumping function drops below 60% or the left ventricle enlarges beyond a certain threshold. For people with symptoms like worsening shortness of breath or exercise intolerance, surgery is indicated regardless of these measurements.