Heart diseases, including atherosclerotic cardiovascular disease and congestive heart failure, are major life-threatening disorders in most countries. Cholesterol is a vital causal factor and focus of research into heart diseases, but the involvement of triglycerides remains unclear. We recently reported a unique patient suffering from severe congestive heart failure and needing cardiac transplantation. Massive accumulation of triglycerides was observed in coronary atherosclerotic lesions as well as in the myocardium, while plasma triglyceride levels were normal. We suggested that this phenotype was a novel clinical entity and named it "Triglyceride deposit cardiomyovasculopathy", or simply "Obesity of the heart". The patient was identified as homozygous for a genetic mutation in the adipose triglyceride lipase, an essential molecule for hydrolysis of intracellular triglycerides. The present paper deals with what we can learn from this single case and discusses its implications for research and clinical medicine related to heart diseases.