Hemodynamically critical ("severe") mitral regurgitation is usually associated with an audible (if not loud) systolic murmur and signs of left ventricular volume overload. However, "silent" severe mitral regurgitation is being increasingly recognized. We review the case histories of nine patients with silent hemodynamically important mitral regurgitation (associated with acute myocardial infarction and chronic valvular, hypertrophic, and ischemic heart disease), six of whom survived mitral valve replacement, of whom five are alive and functioning well more than three years postoperatively. Performance of left ventriculography early in the hospital course of patients with severe unexplained congestive heart failure (with normal or near-normal left ventricular systolic function assessed noninvasively) identifies patients with severe silent mitral regurgitation who may have long-term benefit from mechanical therapy.