Aging is accompanied by a decline in many aspects of cardiovascular function but little is known regarding its influence on myocardial perfusion. Eleven young adults (mean age 25 +/- 4 (s.d.) yr) and 15 older adults (mean age 55 +/- 9 yr) without history or symptoms of cardiovascular disease were studied using H2 15O and positron emission tomography under resting conditions and following administration of intravenous dipyridamole. Myocardial perfusion at rest was similar in the older and younger subjects, averaging 1.17 +/- 0.35 and 1.16 +/- 0.32 ml/g/min, respectively (p = ns). Following dipyridamole, peak myocardial perfusion was blunted in the older subjects, averaging 3.12 +/- 1.09 ml/g/min compared with 4.25 +/- 1.54 ml/g/min in the young adults (p = 0.044). Accordingly, present standards for normal perfusion responses to intravenous dipyridamole may require adjustment for age.