Hearts with compensatory pressure-overload hypertrophy show an increased intracardiac activation of angiotensin II that may contribute to ischemic diastolic dysfunction. We studied whether pressure-overload hypertrophy in response to aortic banding would result in exaggerated diastolic dysfunction during low-flow ischemia and whether the specific inhibition of the cardiac angiotensin converting enzyme by enalaprilat would modify systolic and diastolic function during ischemia and reperfusion in either hypertrophied or nonhypertrophied hearts. Isolated, red blood cell-perfused isovolumic nonhypertrophied and hypertrophied rat hearts were subjected to enalaprilat (2.5 x 10(-7) M final concentration) infusion during 20 minutes of baseline perfusion and during 30 minutes of low-flow ischemia and 30 minutes of reperfusion. Coronary flow per gram was similar in nonhypertrophied and hypertrophied hearts during baseline perfusion, ischemia, and reperfusion. At baseline, left ventricular developed pressure was higher in hypertrophied than nonhypertrophied hearts in untreated groups (224 +/- 8 versus 150 +/- 9 mm Hg; p less than 0.01) and in enalaprilat-treated groups (223 +/- 9 versus 145 +/- 8 mm Hg; p less than 0.01). During low-flow ischemia, left ventricular developed pressure was depressed but similar in all groups. All groups showed deterioration of diastolic function; however, left ventricular end-diastolic pressure increased to a significantly higher level in untreated hypertrophied than in nonhypertrophied hearts (65 +/- 7 versus 33 +/- 3 mm Hg; p less than 0.001). Enalaprilat had no effect in nonhypertrophied hearts, but it significantly attenuated the greater increase in left ventricular end-diastolic pressure in hypertrophied hearts treated with enalaprilat compared with no drug (65 +/- 7 versus 50 +/- 5 mm Hg; p less than 0.01). The beneficial effect could not be explained by differences in coronary blood flow per gram left ventricular weight, glycolytic flux as reported by lactate production, myocardial water content, oxygen consumption, and tissue levels of glycogen and high energy phosphate compounds. During reperfusion, all hearts showed a partial recovery of developed pressure to 70-74% of initial values. No effect of enalaprilat could be detected during reperfusion on systolic and diastolic function or restoration of tissue levels of high energy compounds. In conclusion, our experiments show that hypertrophied red blood cell-perfused hearts manifest a severe impairment of left ventricular diastolic relaxation in response to low-flow ischemia in comparison with control hearts. Further, our experiments support the hypothesis that the enhanced conversion of angiotensin I to angiotensin II in rats with pressure-overload hypertrophy contributes to the enhanced sensitivity of hypertrophied hearts to diastolic dysfunction during low-flow ischemia.