When cardiac hypokinesis in myocardial infarction is analyzed by means of phase analysis of radionuclide (RI) angiography, there are some cases in which the amount of regional wall movement of the left ventricle does not so decline, but the phase delay of regional wall movement is great. Hence, a simulation experiment was performed with a computer to evaluate the influences of regional phase delay on cardiac work. It was assumed that the radius of the model of the left ventricle varies from 3 cm in the late diastolic phase to 2 cm in the late systolic phase, and that in the initial 1/3 time of diastole, the radius alters by 90% of the change. One cardiac cycle (360 degrees) was divided into 60 fractions (1 fraction = 6 degrees), 0 degree being the end of diastole and 180 degrees the end of systole. An ischemic area was supposed to cover S% of the whole volume of the left ventricle, its amount of regional wall movement being P% of the normal area, and the phase delay being R degrees. By varying S, P and R, and taking weighted means of volume curves and normal ones, their assumed volume curves of the left ventricle were computed. Stroke volume (SV) and ejection fraction (EF) obtained from these curves were compared to those obtained from the normal curves, and were expressed in percentage (%SV, %EF). The influences of the changes of S, P and R on the volume curve and on the cardiac work were examined. Then the count curves of the left ventricle (LV) were obtained by gated RI angiography in 22 cases of myocardial infarction and 8 healthy controls, and LV regional wall movements were examined by means of the Fourier analysis. The circular volume was partitioned from the center into eight sections on the LV image of LAO 45 degrees, and the amount of wall movement and the phase delay of each section were evaluated from the count curves of each section. The following results were obtained. %SV and %EF declined with sole occurrence of regional phase delay. Occurrence of the regional phase delay flattened the slope of the volume curve of the initial diastolic phase and formed shoulders on this curve. This was observed also on the count curves actually determined from cases with myocardial infarction. When regional wall movement was markedly decreased, the influence of the regional phase delay on the pattern of the volume curve was slight even if the phase delay was extensive.(ABSTRACT TRUNCATED AT 400 WORDS)