INTRODUCTION: There is an ongoing debate about the impact of endurance exercise on cardiovascular health. Not at least data on cardiac biomarker changes (e.g. troponin T (cTnT), N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and cardiac specific myosin heavy chain-alpha (MHC-α) have raised questions about exercise related cardiac injury. METHODS: In 52 non-elite athletes (14 female, 38 male; age 41.1 ± 9.7, range 24-70 years; all completed the race) biomarkers were measured by standard laboratory methods 7 days before, directly after, and day 1, 4 and 6 after a full Ironman distance triathlon (Swim 3.9 km, Bike 180 km, Run 42.2 km) . In 19 of these athletes (9 female, 10 male) echocardiography with 30 different standard measurements was performed before and directly after the race. RESULTS: Only MHC-α [µg/L] showed a two-peaked increase directly after (2.57 ± 0.78) and on day 4 (2.74 ± 0.55). Other biomarkers showed a one-peaked increase with maximal values either directly after the race or at day 1: cTnT 76 ± 80 ng/L (12-440; reference <15), NT-proBNP 776 ± 684 ng/L (92-4700; ref. < 300), CK 68 ± 55 µkat/L (5-280; ref. < 1.9), MG 2088 ± 2350 µg/L (130-17000; ref.< 72), and creatinine 100 ± 20 µmol/L (74-161; ref. < 100), CRP 49 ± 23 mg/L (15-119; ref.< 5). No significant echocardiographic changes were recorded. E.g. left ventricular end diastolic diameter (49.0 ± 4.7 mm before, 47.7 ± 5.0 mm after the race, right ventricular end diastolic diameter (34.3 ± 4.3 mm before, 33.3 ± 5.7 mm after the race), right atrial area (17.5 ± 2.9 cm2 before, 17.7 ± 3.6 cm2 after the race) and left atrial area (18.8 ± 3.7 cm2 before, 17.8 ± 2.2 cm2 after the race) did not show any significant acute changes. CONCLUSION: While an Ironman leads to remarkable disturbances in biomarkers as e.g. cTnT after the race was in the range of myocardial infarction in 100% of women and 97% of men, these alterations were not correlated to any acute echocardiographic changes in heart size or function. However, the significance of biochemical evidence of cardiac injury on long-term heart function and cardiovascular health remains unclear.