Non-arteriosclerotic (virgin), male and female, Sprague-Dawley rats and arteriosclerotic (breeder), male and female rats were subjected to an acute myocardial infarct when injected with two subcutaneous doses of isoproterenol. Female rats, especially female breeder rats with advanced arteriosclerosis, survived their infarcts in superior fashion to male rats or those with the least severe arterial disease. Animals with severe arteriosclerosis showed the least loss of body weight and greatest increase in heart weight on Day 3 when cardiac necrosis reaches its zenith. Blood pressure and pulse pressure was most seriously reduced in animals with no or early arteriosclerosis only, being best maintained in the animals with the most severe arterial disease. Heart rate was not greatly altered in any of the various groups. Ventricular function, i.e., cardiac output, stroke volume, cardiac index, and left ventricular minute work, was severely impaired in the non-arteriosclerotic animals and in those with the least arterial disease. Total peripheral resistance was also least elevated and myocardial contractile strength (peak flow and max dF/dt) was greatest in female breeders with the most advanced arterial disease. Most intriguing, is the seemingly paradoxical but consistent finding that female breeders which develop the most severe arterial disease are able to best maintain cardiac function during the acute stress of myocardial ischemia.