Under normal circumstances, most energy substrate used for heart contraction derives from fatty acids in the form of nonesterified fatty acids bound to albumin or fatty acids derived from lipolysis of lipoprotein-bound triglyceride by lipoprotein lipase (LpL). By creating LpL knockout mice (hLpL0), we learned that loss of cardiac LpL leads to myocardial dysfunction; therefore, neither nonesterified fatty acids nor increased glucose metabolism can replace LpL actions. hLpL0 mice do not survive abdominal aortic constriction and they develop more heart failure with hypertension. Conversely, we created a mouse overexpressing cardiomyocyte-anchored LpL. This transgene produced cardiac lipotoxicity and dilated cardiomyopathy. Methods to alter this phenotype and the causes of other models of lipotoxicity are currently being studied and will provide further insight into the physiology of lipid metabolism in the heart.