Moderate Normobaric Hypoxia Does Not Exacerbate Left Ventricular Dysfunction After Exhaustive Exercise in Athletes and Untrained Individuals

<b>Background:</b> Exposure to hypoxia is widely used to enhance training adaptations, but its acute effects on cardiac function remain unclear. Exercise-induced cardiac fatigue (EICF), defined as transient impairments in left ventricular (LV) systolic and diastolic function, has been reported after endurance exercise. Whether moderate hypoxia influences EICF, particularly in athletes, is unknown. <b>Methods:</b> Twenty-four healthy men participated: 12 endurance-trained cyclists (T) and 12 untrained individuals (UT). Each completed two exhaustive cycling tests under normoxia (FiO₂ = 20.9%) and moderate normobaric hypoxia (FiO₂ = 14.4%; ~3000 m). Echocardiography was performed at rest and immediately post-exercise to assess LV systolic and diastolic function. <b>Results:</b> Exhaustive exercise reduced LV diastolic function in both groups, with no significant condition-related differences. Under normoxia, early peak filling velocity (Mitral E) decreased by 21.2% in UT and 23.2% in T, and under hypoxia, by 16.2% in UT and 14.9% in T. Global longitudinal strain (LV GLS) became less negative after exercise under normoxia (UT: +25.2%, T: +30.6%) and hypoxia (UT: +24.8%, T: +20.3%). Athletes exhibited slightly less post-exercise systolic impairment under hypoxia than normoxia, reflected by the maintenance of a more negative LV GLS (∆GLS: 6.87 ± 2.65% in normoxia vs. 4.55 ± 1.86% in hypoxia, <i>p</i> < 0.05). <b>Conclusions:</b> Moderate normobaric hypoxia (~3000 m) did not exacerbate EICF in either group. Athletes showed slightly less post-exercise systolic impairment under hypoxia. Moderate hypoxia may modify the cardiac response to exhaustive exercise, but studies with larger samples and direct preload assessment are needed.