This prospective, longitudinal study examined the effects of participation in team-based exercise training on cardiac structure and function. Competitive endurance athletes (EA, n = 40) and strength athletes (SA, n = 24) were studied with echocardiography at baseline and after 90 days of team training. Left ventricular (LV) mass increased by 11% in EA (116 ± 18 vs. 130 ± 19 g/m²; P < 0.001) and by 12% in SA (115 ± 14 vs. 132 ± 11 g/m²; P < 0.001; P value for the compared Δ = NS). EA experienced LV dilation (end-diastolic volume: 66.6 ± 10.0 vs. 74.7 ± 9.8 ml/m², Δ = 8.0 ± 4.2 ml/m²; P < 0.001), enhanced diastolic function (lateral E′: 10.9 ± 0.8 vs. 12.4 ± 0.9 cm/s, P < 0.001), and biatrial enlargement, while SA experience LV hypertrophy (posterior wall: 4.5 ± 0.5 vs. 5.2 ± 0.5 mm/m², P < 0.001) and diminished diastolic function (E′ basal lateral LV: 11.6 ± 1.3 vs. 10.2 ± 1.4 cm/s, P < 0.001). Further, EA experienced right ventricular (RV) dilation (end-diastolic area: 1,460 ± 220 vs. 1,650 ± 200 mm/m², P < 0.001) coupled with enhanced systolic and diastolic function (E′ basal RV: 10.3 ± 1.5 vs. 11.4 ± 1.7 cm/s, P < 0.001), while SA had no change in RV parameters. We conclude that participation in 90 days of competitive athletics produces significant training-specific changes in cardiac structure and function. EA develop biventricular dilation with enhanced diastolic function, while SA develop isolated, concentric left ventricular hypertrophy with diminished diastolic relaxation.