Introduction: Androgenic anabolizing steroids (AAS) are a group of natural and synthetic compounds deriving from testosterone or one of its sub-products which are more and more used by young people for improving physical performance or for aesthetic reason. Complications, such as arteriosclerosis and acute myocardium infarction (AMI), have been reported in AAS’ users, but the records about the ventricular anatomical structure of those users are few. Because of that, this study aimed to verify morphologic and quantitative morphometric possible alterations on mice’s left ventricular myocardium submitted to their use. Materials and Methods: Thirty mice were divided into three 10-animals groups (group 1: received Deca-Durabolin ? ; group 2: received Potenay ? ; and group 3: received saline solution), each one of them composed by five males and five females, treated once a week and put to swimming thrice a week during one month. Results: Results revealed that there were no significant alterations in the quantity of muscle fibers in the animals treated with AAS but there were significant differences when comparing male-to-female mice and left ventricular area (?m2). It was observed that mice in group 1 (Deca-Durabolin ? ) presented a lesser left ventricular area when compared to those in group 3 (control) but, when analyzing cardiac muscle fibers morphologically, it was verified that the myocardium was looser and softer in drug-submitted animals, especially those in group 1 (Deca-Durabolin ? ). Conclusion: There are effective significant differences when a morphologic and quantitative morphometric analysis is done concerning mice’s left ventricular myocardium submitted to AAS.