Regional systolic bulging during early systole has been reported to be present frequently in regions with ischmic or scarred myocardium. To sturdy the mechanisms of the systolic bulging and effects of isosorbide dinitrate (ISDN) and nifedipine on the systolic bulging, we conducted resting gated radionuclide venticulographic study (RIVG) and Tl-201 myocardial scintigram in 35 patients with old anteroseptal myocardial infarction (ASMI), 16 and 10 patients of them also underwent RIGV after ISDN or after nifedipine , respectively. A computer program subdivided the image of the LV into 4 regions, and the time-activity curves in the global LV, septal, and lateral regions were used for analysis. The degree of the systolic bulging (%Bulging) was calculated as follows : %Bulging＝ [(maximal－LV－C)(ED－LV－C)] / [(ED－LV－C)(ES－LV－C)] ＊ 100] LV－C ; regional LV counts. ED ; end diastolic. ES ; end systolic. In ASMI, the systolic bulging was found in the septal region, and %Bulging was 8.4±4.5%. The septal EF was positively correlated with the septal Tl uptake ratio (r＝0.79, p＜0.001). The %Bulging had no correlation with the septal EF and the septal Tl uptake ratio. Although ED volumes (EDV) and the %Bulging showed no change after nifedipine, the %Bulging increased from 8.0±6.6% to 23.7±23.0%(p＜0.05) and EDV slightly decreased after ISDN. The change in the %Bulging was positively correlated with the change of peak ejection rate of the lateral region (r＝0.59). Thus, the septal EF is dependent on the degree of vibility of the septal myocardium, but the %Bulging is not dependent on it. Then, the systolic bulging in the infarcted region is exaggerated after ISDN, which cause may be due to preload reduction, and its degree is probably deoendent on the function in the normal perfused region. And the mechanisms of the systolic bulging is regional agterload due to an intraventricular mechanical interaction between ischemic and non-ischemic regions. Besides, we found that ISDN and nifedipin have different effects on the regin wall motion of ischemic regions in early systole.