It has been suggested that the decline of cardiac output with age is due to increased prevalence of disease, particularly occult coronary artery disease. Therefore, the relation of cardiac output (direct oxygen Fick method) to age was analyzed in 110 sixteen- to 64-year-old men with World Health Organization stage I or II essential hypertension at the time of the hemodynamic study, who were alive and free of cardiovascular complications 7 years later. At supine and seated rest, during upright bicycle exercise at 50 W and and at peak work load, cardiac output was inversely (p less than 0.01) related to age. These relations were independent of weight and mean intraarterial pressure. Stroke volume decreased with advancing age at supine rest, but not at rest and during exercise in the seated position. Heart rate was not affected by age in the supine position, but was slower in older patients during upright rest and at peak exercise. In conclusion, in patients with essential hypertension who remained free of cardiovascular complications for 7 years, cardiac output was independently and inversely related to age at various levels of activity. These findings suggest that occult cardiovascular disease does not explain the decline in cardiac output with age in patients with essential hypertension.