A 36-year-old male chimpanzee (Pan troglodytes) assigned to a life-long sign language communication project presented for sudden death. No other clinical or clinical pathological abnormalities were noted and given the signalment, death due to cardiac failure was suspected. Necropsy findings revealed moderate cardiomegaly and other chronic age-related findings including focal renal tubular cystic dilation and gingival hyperplasia. Histologic evaluation of the heart revealed interstitial fibrosing cardiomyopathy characterized by severe interstitial myocardial fibrosis replacing and separating myofibers within all chambers of the heart, especially the left ventricle, interventricular septum and subvalvular areas. This case report represents an additional case of sudden death associated with interstitial myocardial fibrosis in a chimpanzee. This process has been previously cited as the most common cause of sudden death in aged chimpanzees.