The effect of long-term pressure overload on myocardial functional and metabolic alterations was investigated in hearts from spontaneously hypertensive rats of 16 weeks (young SHR) and 44 weeks (aged SHR) and age matched normotensive Wistar Kyoto strain rats (young WKY, aged WKY). The hearts were perfused by working heart mode and whole heart ischemia was induced by one-way valve. Following 20 min of ischemia, the hearts were reperfused for 30 min. The heart-body weight ratio in both SHR groups was significantly higher than in the respective age-matched WKY groups. Coronary flow relative to heart weight in both SHR groups was significantly lower than that of the respective age-matched WKY during both preischemic and reperfused periods. There was no significant difference in the recovery rate of cardiac output between young and aged WKY, whereas the young and aged SHR revealed significantly less recovery than their respective age-matched WKY. Tissue creatine phosphate and energy charge in both aged groups were significantly lower than in the young groups. These results indicate that long-term pressure overload increases susceptibility to ischemia and decreases the myocardial reserve presumably resulting from relative ischemia, whereas deterioration was minimal in the normotensive aged rat heart.