Abstract Obesity is increasing at an alarming rate globally. Several studies have shown that premenopausal women have a reduced risk of CV disease and a reduced myocardial susceptibility to ischaemia/reperfusion injury. The effect of obesity on myocardial tolerance to ischaemia in women has not been established. To determine how obesity affects myocardial susceptibility to ischaemia/reperfusion injury in both males and females, we fed male and female Wistar rats a high caloric diet (HCD) or a control rat chow diet (CD) for 18 weeks. Rats were subsequently fasted overnight, anesthetized and blood was collected. In separate experiments, 18 week fed (HCD and CD) rats underwent 45 minutes in vivo coronary artery ligation (CAL) followed by 2 hours reperfusion. Hearts were stained with TTC and infarct size determined. Both male and female HCD fed rats had increased body and visceral fat weights. Homeostasis model assessment (HOMA) index values were 13.95 +/- 3.04 for CD and 33.58 +/- 9.39 for HCD male rats (p < 0.01) and 2.98 +/- 0.64 for CD and 2.99 +/- 0.72 for HCD fed female rats. Male HCD fed rats had larger infarct sizes than CD fed littermates (43.2 +/- 9.3 % vs. 24.4 +/- 7.6 %, p < 0.05). Female HCD and CD diet fed rats had comparable infarct sizes (31.8 +/- 4.3 % vs. 23.9 +/- 3.3 %). We conclude that male rats on the HCD became viscerally obese, dyslipidaemic and insulin resistant while female HCD fed rats became viscerally obese without developing dyslipidaemia or insulin resistance. Obesity increased myocardial infarct size in males but not the females.