The etiology and clinical significance of asynchronous relaxation of the left ventricle during isovolumic relaxation period was studied. Fifty patient with angina pectoris, 50 with myocardial infarction, 40 with normal heart, 20 with mitral stenosis and 10 with mitral prolapse syndrome were investigated. Asynchronous relaxation was observed in the following order: 72% in angina pectoris, 46% in myocardial infarction, 30% in mitral valve prolapse and 10% in both pure mitral stenosis and normal heart. In left anterior descending coronary artery disease, asynchronous relaxation was observed in 80%. Asynchronous relaxation seen before aortocoronary bypass graft to the left anterior descending coronary artery either disappeared or decreased after surgery. The contractility of the site, where asynchronous relaxation was seen, was normal in most cases and akinetic in none. The results of this study suggest the possibilities that asynchronous relaxation is at least partially related to localized myocardial ischemia and that it may be an early phenomenon of the effect of myocardial ischemia. With regard to asynchronous relaxation and hemodynamic alterations, force-velocity lissajous was analysed. Distortion of the lissajous in relaxation phase was seen in 73% who showed asynchrony. This distortion can be interpreted as indication of ununiformity of the left ventricular relaxation.