Four patients with old myocardial infarction (OMI) revealed exertional hypotension in the treadmill exercise test. All had a multivessel disease, severe left ventricular dysfunction and exercise-induced ST depression or angina to indicate additional myocardial ischemia. After 5 mg of oral isosorbide dinitrate (ISDN), the response of blood pressure was improved with a delayed onset of ST depression or angina. To confirm the effect of ISDN on the pressure response to exercise, 26 patients with OMI were further studied. In patients without ST depression and angina (Group I), the systolic blood pressure (SBP) at the matched work load was significantly decreased after ISDN. However, in patients with ST depression or angina (Group II), SBP at the matched work load was not altered after ISDN. The increment of change in SBP due to ISDN, namely from the resting level to the matched work load, was significantly larger in Group II than in Group I. In addition, the patients with marked left ventricular dysfunction in Group I revealed a more change in SBP due to ISDN than the others in Group I. It was concluded that exertional hypotension or suppressed pressure response of OMI could be corrected by 5 mg of oral ISDN due to its favorable effects on the exercise-induced myocardial ischemia and preexisting left ventricular dysfunction.