Purpose: Despite potential severe cardiac side effects, anabolic androgenic steroids (AAS) are increasingly used by strength athletes. However, previous echocardiographic studies focused on the left ventricular strains (LV) but did not assess LV twist and untwist mechanics. Moreover, LA function has been often neglected, and its stiffness, an important determinant of LA reservoir function, has never been challenged. The aim of this study was to investigate the effects of anabolic androgenic steroids (AAS) on left atrial (LA) and left ventricular (LV) morphologies and functions in strength athletes. Methods: 50 subjects including 20 strength-trained young athletes aged 32.0 ± 8.5 years with a mean duration of AAS use of 4.7 ± 1.8 years (Users), 15 athletes with no history of AAS use (Non-Users) and 15 sedentary controls underwent STE to assess LA and LV morphology and function. Results: Users showed higher LA reservoir dysfunction than Non-Users (33.7 ± 10.9 vs 44.9 ± 9.9 % respectively, p = 0.004) and higher LA stiffness (0.13 ± 0.05 vs 0.19 ± 0.08 A.U. respectively, p = 0.02), higher LV mass index and lower global and regional LV diastolic and systolic dysfunction (global longitudinal strain: -15.5 ± 3.2 vs -18.9 ± 1.8 % respectively, p = 0.003), with a drop of LV twist-untwist mechanics (untwisting velocity: 61.5 ± 20.2 vs 73.7 ± 16.1 deg.s-1 respectively, p = 0.04). There were significant correlations between LV mass and LV apical rotation (p = 0.003, r = 0.44) and diastolic longitudinal strain rate (p = 0.015, r = 0.33). Conclusion: Our results showing significant LA and LV remodeling and dysfunctions in young AAS using athletes are alarming. Screening echocardiography based on STE parameters for early diagnosis, as well as a stronger awareness in athletes and in physicians are warranted in this context.