Backgroung: Levo-Carnitine is known L-carnitine that is generally used in medical and nutritional fields. Recent studies highlightened L-carnitine-induced cardiovascular toxic effects. Trimethylamine-N-oxide (TMAO) and heart-type fatty acid-binding protein 3 (HFABP3) are risk markers of its toxicity. Aim of this study was to elucidate the relationship between L-carnitine metabolites and cardiac damage biomarkers in L-carnitine supplemented students. Patients and Methods: 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 done for all of them. These students have been investigated for L-carnitine, cardiac troponin I (cTn-I), H-FABP3, and TMAO levels. Results: All markers have been significantly elevated when compared with those of the control group. ECG findings were ST depression in 24 students (49%), and T wave inversion in 1 9 students (38.8%) where sinus tachycardia was the commonest finding (77.6%). Furthermore, L-carnitine showed a significant positive correlation with H-FABP3, TMAO, cTn-I, and heart rate. Conclusion: TMAO, HFABP3 seem to be the strongest predictors for long term L-carnitine supplementation's cardiovascular toxicity. Further studies to assess both the efficacy and long term safety of oral L-carnitine supplementation for atheletes that used for physical enhancement were recommended.