This experiment was undertaken to assess the effect of nitric oxide, isosorbide dinitrate, and sodium nitroprusside, which are known to increase coronary flow by vasodilation and to improve the cardiac function of an ischemic heart The experiment was carried out to investigate the effect of nitric oxide on the coronary artery of an ischemic rat myocardium using isolated constant pressure Langendorfr system. The experimental parameters were lactate and CK-MB for the frozen myocardium and coronary flow. the quantity of coyonary flow, left ventricular developed pressure (LVDP), and dp/dt. The experimental groups were decided as control group (Group I), nitric oxide group (Group II), Iso orbide dinitrate group (Group III) and sodium nitroprusside group (Group IV). Statistical analysis was performed using repeated measured analysis of variance and 2tudent t-test The results were as follows: 1 . The lactic acid contents of group II and IV were less than other groups for the frozen myocardium at preischemic state (p< 0.0025), whereas the determined coronary flows were higher. 2. In the ratio of produced lactic acid between the preischemia and reperfusion for the coronary flow, group II and IV exhibitrod less value than others (p< 0.005). 3. Group II and III were less than others in the coronary flow for the quantity of CK-MB, but or the frozen myocardium, group II and IV were less. 4. Group II and IV showed higher coronary flow compared to others throughout entire experimental period (p< 0.005). 5. Group II was highest at the preischemic state for the left ventricular developed pressure. 6. The +maximal dp/dt of group II was highest compared to others. 7. Group I exhibi ed the highest recovery rate of coronary flow between prelschemla and reperfusion. 8. The(-dp/dt)1(+dp/dt) ratio was 116%, 100%, 100%, and 55% for the 4 groups, respectively And the recovery rate of total dp/dt was 34%, 67%, 51%, and 76% for the four groups, respectively.