The effect of aging on cardiac function in patients with right bundle branch block (RBBB) was commonly unknown, so left ventricular function and right ventricular function were investigated, using first-pass radionuclide angiography. Twenty-six patients with RBBB and 28 normal subjects were studied at rest and during bicycle exercise. Patients with RBBB but normal cardiovascular systems aged 33 to 75 years were divided into those within 60 years (n = 17) and those over 65 years (n = 9). Using the same method, normal subjects aged 38 to 83 years were divided into those within 60 years (n = 18) and those over 65 years (n = 10). Mean age between normal subjects and patients with RBBB didn't differ significantly. The response of left ventricular ejection fraction in normal groups rose during exercise, but its exercise tolerance function declined with aging. Left ventricular diastolic filling in normal groups declined at rest and during exercise with aging. Left ventricular function in RBBB groups showed the same results as those of normal groups. The response of right ventricular ejection fraction and its exercise tolerance function in normal groups was not influenced by aging. However, in contrast, right ventricular function in RBBB groups decreased with aging. We suggest that the mechanism of decrease of right ventricular function in aging patients with RBBB may be caused by the change of right ventricular contraction which is affected by the aging process.