The purpose of this study was to examine cardiac function following a 100-mile ride in high ambient temperatures by healthy, competitive cyclists. Methods: Subjects were six (n=6) competitive cyclists racing in a 100-mile road race. Measures (pre/post) included: body mass (kg); E:A ratio (ventricular compliance); stroke volume (ml); ejection fraction (%) through echocardiography; age (y); training status (hrs*week[superscript -1]); years of racing experience (YE); race finish time (hrs); height (cm); mean race heart rate (b*min[superscript -1]), and post race blood troponin I (cTnI) to assess myocyte damage. Results: subject means ([plus or minus]SE) were the following: age, 24.2 (1.2) y; height, 181.1 (5.5) cm; training status, 18 (2.4) hrs*week[superscript -1]; racing experience, 5.8 (4.6) y; race heart rate, 159.3 (3.9) b*min[superscript -1]; pre/post E:A ratio, 2.04(0.41)/1.27(0.39); pre/post stroke volume, 98.6 (21.6)/72.6(11.8) ml*min[superscript -1]; cTnI, 0.13 (0.15); ejection fraction pre/post, 67.3 (3.8)/65.1(2.2)%; finish time 4.05 (0.54) hrs. Significant (p less than 0.05) differences were determined pre/post for E:A ratio, stroke volume, and pre/post body mass, 76.4 (5.9)/72.4 (1.8) kg. cTnI was elevated above established levels of 0.03 ng*ml[superscript -1] for cellular disruption. Conclusion: The differences in E:A ratio (i.e., ventricular compliance), stroke volume and elevated cTnI indicate reduced cardiac function indicative of cardiac fatigue. (Contains 1 table and 3 figures.)