Introduction: Anabolic-androgen steroids (AAS) associated with physical training induce changes from physiological cardiac hypertrophy (CH) to pathological hypertrophy. However, these studies were performed with strength athletes, and the AAS effects associated with aerobic training are still poorly understood. Thus, the aim of this study was to evaluate the effects of aerobic training and AAS on the cardiac structure and function. Methods: 28 Wistars rats divided in 4 groups were used: sedentary control (SC), sedentary anabolic (SA), trained control (TC) and trained anabolic (TA). The AAS was administered twice a week (10mg/Kg/week). The swimming training was conducted 5 sessions per week during 10 weeks. We evaluated blood pressure and heart rate by tail plethysmography, ventricular function by echocardiography, cardiomyocyte diameter and collagen volumetric fraction by histological methods. Results: There were no differences in BP. TC group showed reduction in rest heart rate after the experimental period, which did not occur in TA group. CH of 38% in SA group; 52% in TC group and 64% in TA group compared to SC group was observed. TA group presented decrease in diastolic function in relation to other groups. The trained groups showed significant increases in cardiomyocytes diameter. SA and TA groups showed increase in collagen volumetric fraction in relation to SC and TC groups. Conclusion: The results show that AAS treatment associated to swimming training induces CH, mainly by the increase in interstitial collagen, which can lead to loss of diastolic function.