This study assesses the effect of aging on human myocardial morphology. Fifteen patients, ranging in age from 28 to 75 with normal cardiac history, physical examination and noninvasive tests of left ventricular function, underwent right ventricular endomyocardial biopsy prior to cancer chemotherapy. Cell diameter, nuclear area and fibrosis were quantified by light microscopy. Semiquantitative methods of electron microscopy were used to grade lipofuscin deposition, tubular dilation, myofibrillar loss, folding of discs and lipid deposition. The results demonstrated that myocardial cell diameter correlated directly with age (r = 0.73, p less than 0.01) and systolic blood pressure (r = 0.51, p less than 0.05). Nuclear area (r = 0.76, p less than 0.01) and folded discs (r = 0.53, p less than 0.05), two signs of increased protein production also correlated with age. Lipid deposition (r = 0.40), tubular dilation (r = 0.31) and lipofuscin deposition (r = 0.20) increased with, but did not correlate significantly with age. Lipid deposition (r = 0.56, p less than 0.05) and tubular dilation (r = 0.43, p less than 0.05) did correlate with cell diameter. Thus, the aging myocardium is characterized by increased cell size and some degenerative changes.