mitral regurgitation

Imagine pushing a syringe but the plunger seal leaks, so some fluid squirts back past it instead of going forward. In mitral regurgitation the mitral valve does not seal during systole, so when the left ventricle contracts, part of the blood meant to go forward into the aorta instead leaks backward into the left atrium.

Each heartbeat therefore wastes some of its work, and the leaked blood overloads the left atrium and then the left ventricle, which must pump a larger volume to deliver an adequate amount forward. Over time both chambers enlarge. Chronic regurgitation may be silent for years before causing breathlessness and fatigue, whereas acute severe regurgitation — for instance from a ruptured chord or after a heart attack — can flood the lungs suddenly.

Causes are divided into primary, where the valve apparatus itself is faulty (degeneration, prolapse, rheumatic disease, infection), and secondary or functional, where a dilated or poorly contracting ventricle pulls the leaflets apart even though the valve is structurally normal. Echocardiography with Doppler grades the leak; severe primary regurgitation is often treated by surgical repair, which is generally preferred to replacement when feasible.

Distinguishing primary from secondary disease matters greatly for treatment, which is individualized and beyond the scope of this reference.