This study examined the effects of anabolic steroids and exhaustive endurance exercise, and the combination of both treatments on in vitro cardiac contractile function. Fifty-two male Sprague-Dawley rats were randomly assigned, in groups of 13, to one of the four groups: sedentary control (C), steroid-treated (ST), exercise-trained (E), and exercise plus steroid treated (E + S). Nandrolone decanoate was administered to the steroid-treated groups every 7-9 days during the 10 weeks study, while the C and E groups received glycerol injection on these occasions. The exercised rats ran on a treadmill wearing a collar weight (2-3% of body weight) for 50 min, 5 days a week. In vitro ventricular performance was assessed in isolated Langendorff perfused hearts in response to increasing left ventricular balloon volumes. Left ventricular +dP/dt, dP/dt at 60 mmHg developed pressure, tension time index, and Emax (slope of the pressure-volume curves) were significantly (p<0.05) lowered in the E + S group, as compared to the C, E, or ST group. Meanwhile, the E group exhibited a higher (p<0.05) left ventricular systolic pressure (LVSP) than the C and E + S groups. No significant differences in dP/dt/P, heart weight (wt), and heart wt to body wt ratio were detected among the four groups. Rats subjected to endurance exercise or anabolic steroid treatment alone exhibited no change in LV function. It is concluded that 1) anabolic steroid treatment in combination with endurance exercise produced a depressive effect on cardiac contractile function when compared to endurance exercise training or steroid treatment alone, and 2) cardiac contractile function was not altered following endurance exercise training or anabolic steroid treatment alone.