A67-year-old man underwent transthoracic echocardiography for the evaluation of heart failure. The echocardiographic examination demonstrated significant dilatation of all cardiac chambers with marked global left ventricular (LV) systolic dysfunction (LV ejection fraction of 10% to 15%). Color flow imaging revealed a mild-to-moderate degree of mitral regurgitation (MR). Diastolic as well as systolic MR was detected by multiple Doppler modalities (Figures 1 to 3⇓⇓⇓). Diastolic MR resulted from the combination of first-degree atrioventricular (AV) block and severe elevation of LV filling pressures. Effective ventricular contraction is mandatory for complete mitral valve closure. Diastolic MR is commonly observed during AV block of any degree, when atrial contraction is not followed by adequately synchronized LV contraction. Under these conditions, the AV pressure gradient reverses during …