Levo-Carnitine (L-carnitine) is generally used in health and food. Recent studies focused on L-carnitine-induced cardiovascular toxicity. Trimethylamine-N-oxide (TMAO) and heart-type fatty acid-binding protein 3 (HFABP3) are risk markers of its toxicity. The aim of this study was to elucidate the relationship between L-carnitine metabolites and cardiac damage biomarkers in L-carnitine supplemented students. This study was carried out on students at tennis section, faculty of physical education for girls, Zagazig University. These students were divided into 2 groups. Group I: Forty nine healthy individuals (age- and grade-matched), and group II: Forty nine L-carnitine supplemented students (1000mg/day in 2 or 3 divided doses orally). Clinical examination and electrocardiography (ECG) were performed for all of them. These students have been investigated for cardiac damage biomarkers; cardiac troponin I (cTn-I), heart-type fatty acid binding protein 3 (H-FABP3). L-carnitine and its metabolites TMAO have been also assessed. All biomarkers have been measured and compared with those of the control groups. ECG findings were ST depression in 24 students (49%), and T wave inversion in 19 students (38.8%) where sinus tachycardia was the commonest finding (77.6%). There was a statistically significant increase of L carnitine, TMAO, HFABP3, and cTn-I levels. Furthermore, L-carnitine showed a significant positive correlation with H-FABP3, TMAO, cTn-I, and heart rate. TMAO, HFABP3 seem to be the strongest predictors for long term L-carnitine supplementation's cardiovascular toxicity. Further studies to evaluate both the efficacy and long term safety of oral L-carnitine supplementation for atheletes for physical enhancement were recommended.