We examined the effect of intensity during prolonged exercise (PE) on left and right ventricular (LV and RV) function . Subjects included18 individuals (mean ± SEM: age=28.1 ± 1.1 years, VO_2max=55.1 ± 1.6 ml^.kg^-1.min^-1),who performed 150 min exercise at 60% and 80% VO_2max on two separate occasions. Transthoracic echocardiography assessed systolic and diastolic performance and blood sampling assessed hydration status and noradrenaline (NA) levels before (pre), during (15 and 150 min), and 60 min (post) following PE.. -adrenergic sensitivity pre and post PE was assessed by dobutamine stress. High-intensity PE (15 vs. 150 min) induced systolic reductions in LV EF (69.3 ± 1.3% vs. 63.5 ± 1.3%, p=0.000), LV strain (-23.5 ± 0.6% vs. -22.3 ± 0.6%, p=0.034), and RV strain (-26.3 ± 0.6% vs. -23.0 ± 0.6%, p<0.01). Both exercise intensities induced diastolic reductions (pre vs. post) in E'/A'septal (2.15 ± 0.15 vs. 1.62 ± 0.09; 2.21 ± 0.15 vs. 1.48 ± 0.10), E'/A'lateral (3.84 ± 0.42 vs. 2.49 ± 0.20; 3.56 ± 0.32 vs. 2.08 ± 0.18), LVSRe/SRa (2.42, ± 0.16 vs. 1.97 ± 0.13; 2.30 ± 0.15 vs. 1.81 ± 0.11) and RVSR_e/SR_a (2.03 ± 0.17 vs. 1.51 ± 0.09; 2.16 ± 0.16 vs. 1.44 ± 0.11 )(p<0.001). Evidence of -adrenergic sensitivity was supported by a decreased S, SR, EF, and SPVR response to dobutamine (p<0.05) with elevated NA (p<0.01). PE-induced reductions in LV and RV systolic function, were related to exercise intensity and -adrenergic desensitization. The clinical significance of exercise induced cardiac fatigue warrants further research.