Anabolic-androgenic steroids (AAS) are used by power athletes to improve performance. However, the real effects of the chronic consumption of AAS on cardiovascular structures are subjects of intense debate. To detect by speckle tracking echocardiography (STE) underlying left atrial (LA) dysfunction in athletes abusing AAS and assess possible correlation between LA myocardial function and exercise capacity during cardiopulmonary stress test. 65 top-level competitive bodybuilders were selected (45 males), including 35 athletes misusing AAS for at least 5 years (users), 30 anabolic-free bodybuilders (non-users), compared to 40 age- and sex-matched healthy sedentary controls. Standard Doppler echocardiography, STE analysis and bicycle ergometric test were performed to assess LA myocardial function and exercise capacity. Athletes showed increased left ventricular (LV) mass index, wall thickness and stroke volume compared with controls, whereas LV ejection fraction, LV end-diastolic diameter and transmitral Doppler indexes were comparable between the three groups. Conversely, LA volume index, LV and LA strain and LV E/Em were significantly increased in AAS users. By multivariate analyses, LV E/Em (beta = - 0.30, p < 0.01), LA volume index (- 0.42, p < 0.001) and number of weeks of AAS use per year (- 0.54, p < 0.001) emerged as the only independent determinants of LA lateral wall peak STE. In addition, a close association between LA myocardial function and VO peak during cardiopulmonary exercise testing was evidenced (p < 0.001), showing a powerful incremental value with respect to clinical and standard echocardiographic data. STE represents a promising technique to assess LA myocardial function in athletes abusing steroids. AAS users showed a more impaired LA deformation, associated with reduced functional capacity during physical effort.