To clarify the significance of regional myocardial perfusion, 31 patients of old myocardial infarction including 11 cases undergoing PTCA with a left anterior descending artery lesion were studied using dynamic transmission computed tomography with excellent time resolution. Serial one-second dynamic scans with an electrocardiographic triggering system were performed at the middle level of the left ventricle using a bolus injection of contrast medium via the inferior vena cava. The F/V (F = flow, V = volume) ratio, a parameter of perfusion per unit of myocardium, was calculated from gamma-variate fitted time density curves obtained in the myocardium and in the left ventricular cavity. The F/V ratio was significantly lower in patients not only with severe but also mild and no coronary artery stenosis (post PTCA: 185 +/- 54, 50-75% stenosis: 193 +/- 47, 90% stenosis: 181 +/- 51, 99% stenosis: 140 +/- 34, 100% stenosis: 142 +/- 27 ml/min/100 g, control value: 243 +/- 51 ml/min/100 g, post PTCA, 50-75% stenosis, 90% stenosis vs control p less than 0.05, 99%, 100% stenosis vs control p less than 0.005). The functional images depicting myocardial perfusion frequently revealed abnormal perfusion findings in patients not only with severe but also mild and no coronary stenosis. In the patients with mild or insignificant coronary stenosis, the F/V ratio was dependent on the severity of left ventricular wall motion abnormalities (hypokinesis: 192 +/- 51, akinesis or dyskinesis: 141 +/- 32 ml/min/100 g; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)