L-Carnitine is an endogenous quaternary ammonium compound required for fatty acid transport; it is often given as a dietary supplement. The L-isomer is active, exhibiting anti-osteoporotic, antioxidative, and cardioprotective activities. In a clinical setting, L-carnitine administration increases muscle carnitine content and work output while decreasing glycogen utilization during exercise. Additionally, L-carnitine improves postprandial flow-mediated dilation, slightly increasing vascular function. In animal models, L-carnitine increases bone mineral density and decreases bone resorption. L-Carnitine also improves plasma markers of exercise stress such as malondialdehyde. L-Carnitine improves symptoms of cardiovascular disease accompanying myocardial infarction and decreases ventricular arrhythmias, symptoms of angina, and mortality rates.