chronic administration of high doses of Anabolic Androgeic Steroids (355.4 +/- 59.47 mg.wk) lead to hemodynamic and metabolic response impairment. In conclusion, the chronotropic significant incompetence in the current study was reflected by an exaggerated hemodynamic response to exercise. Furthermore, the findings suggest that nonusers of AAS showed increases in VO2max when compared to the AAS group. Therefore, this study provides a contraindication to AAS use, especially in those at increased risk of cardiovascular events.
So, they make you more prone to heart attacks plus they stop you improving your VO2mx.