A patient of faintly marfanoid habitus with left venticular failure, aortic regurgitation, and rate-related left bundle-branch block was found to have a midsystolic click and echocardiographic findings suggestive of mitral valve prolapse; however, the click did not move earlier in systole in response to head-up tilt or atrial pacing. Cardiac catheterization and angiocardiographic studies revealed severe left ventricular dysfunction out of proportion to the moderate amount of aortic regurgitation observed on aortographic study. Mitral valve prolapse was not confirmed by left ventriculographic study. Intracardiac phonocardiographic and catheter-tip manometric studies identified the click as being aortic in origin, ejection in timing, and midsystolic, rather than early systolic, because of delayed aortic valve opening related to left ventricular dysfunction and delay in conduction.