Patients with MS typically present more than 20 years after an episode of rheumatic fever. Single or recurrent bouts of rheumatic carditis cause progressive thickening, scarring, and calcification of the mitral leaflets and chordae (Figure 1). Fusion of the commissures and chordae decreases the size of the mitral opening (Figure 2). This obstruction results in the development of a pressure gradient across the valve in diastole and causes an elevation in left atrial and pulmonary venous pressures. Elevated left atrial pressures lead to left atrial enlargement, predisposing the patient to atrial fibrillation and arterial thromboembolism. Elevated pulmonary venous pressure results in pulmonary congestion and pulmonary edema. In advanced MS, patients develop pulmonary hypertension and right-sided HF.