Both in the USA and worldwide, the most common cause of mitral valve pathology in adults is rheumatic fever (RF). Postrheumatic structural changes to the mitral valve typically occur over the 2–10 years following infection, with symptoms appearing over the subsequent 5–10 years. In descending order, secondary etiologies include myxomatous degeneration, endocarditis, idiopathic annular calcification, connective tissue disorders (Marfan syndrome and Ehlers–Danlos syndrome), and hypertrophic cardiomyopathy; however, mitral stenosis (MS) is almost exclusively attributable to rheumatic fever. The onset of decompensated heart failure in MS patients is typically presaged by decreased exercise tolerance with progressive dyspnea secondary to low cardiac output, pulmonary hypertension, and decreased lung compliance. Timely operative intervention early in the symptomatic period can completely reverse heart failure. Mitral regurgitation (MR), where the valve is almost purely regurgitant, is also caused by RF. Ischemic MR is present in up to 20% of patients with coronary artery disease (CAD) requiring operative coronary artery bypass (CAB), and infrequently involves the catastrophic event of ruptured papillary muscle.