Objectives: Over the past two decades, a large interest in cardiac marker elevations has developed in endurance sports events. The intense effort is not without risk. We aimed to see if the relatively cardiospecific biomarkers could show the damage on cardiac muscle cells. Methods: Fourteen cyclists were recruited for an international race (177 km). We studied different cardiac biomarkers, renal function markers and blood cytology. The subjects were submitted to three blood test: one before (T0), one just after (T1) and the last one 3 hours after the race (T3). Results: Blood cytology markers, namely erythrocytes, hemoglobin, hematocrit, and average hemoglobin concentration, were found to evolve in a similar way. Renal function markers, such as creatinin, cystatin C and uric acid, showed a post effort increase that might be related to renal blood flow depletion during exercise. Cardiac and muscular markers were all increased at T1. Conclusions: Physiological stress induced by an international cycling race certainly has consequences on cardiac muscle cells. Fortunately, those blood concentration variations are more representative of a transitional state, due to an imbalance created by an intense aerobic effort maintained during several hours, rather than an irreversible injury.