Habitual exercise results in a rightward shift in left ventricular end diastolic (LVED) pressure-volume or internal dimension (P-D) relationships [left ventricular (LV) remodeling]. However, exercise-mediated LV hypertrophy (LVH) produces an increased LV relative wall thickness [ratio (h/r) of wall thickness (h) to internal radius (r)] and hence a decrement in diastolic wall stress despite LV remodeling. In this study, the effect of chronic administration of an androgenic steroid on exercise-induced LV remodeling and h/r was examined in rats. Habitual exercise on voluntary running wheels resulted in LVH and a rightward shift in the LVED P-D relationships. However, LVH was sufficient to increase LVED h/r. Androgenic steroid administration to exercised rats, without influencing the development of exercise-induced LVH, produced a further rightward shift in the LVED P-D relationship associated with an increased diameter intercept. As a consequence, LVED h/r was reduced to control values. The steroid-mediated effects were not associated with alterations in either the quantity or quality of LV collagen. In conclusion, high-dose androgenic steroid administration alters exercise-induced LV remodeling and subsequently reduces the beneficial effect of physiological LVH on LV h/r.