Various congenital and acquired forms of heart disease have been reported in captive lowland gorillas, and heart disease is a major cause of morbidity and mortality in geriatric humans. However, the prevalence of heart disease is unknown in nonhuman great apes species. Indeed, little is known about heart disease in chimpanzees, although the species has been used in research for decades. This report details the clinical presentation and diagnostics (thoracic radiography, electrocardiography, and echocardiography) utilized to diagnose idiopathic dilated cardiomyopathy in a 27-year-old male chimpanzee. Treatment decisions--indicated by follow-up diagnostics including repeat electrocardiography, echocardiography, and clinical laboratory data--over the 22-month period during which he continues to be treated are described. In addition, electrocardiographic and echocardiographic findings obtained from 20 clinically normal adult (11 female and 9 male) chimpanzees are presented for comparison.