The capacity to secrete human atrial natriuretic peptide (hANP) in response to atrial pacing and the resulting changes in diuresis and urinary electrolyte excretion were compared in children with and without a ventricular septal defect (VSD). The subjects examined were 9 children with a history of Kawasaki disease (as controls) and 11 patients with a VSD, including 5 patients with congestive heart failure (CHF). Their ages ranged from 6 to 40 months old. Atrial pacing resulted in a significant increase in the plasma hANP level from 40 +/- 19 to 140 +/- 37 pg/ml in the controls and from 757 +/- 762 to 1540 +/- 1160 pg/ml in the VSD patients. In control children, the urinary flow rate increased 2.3-fold, urinary sodium excretion increased 6.2-fold and urinary chloride excretion increased 7.6-fold, but these values increased only slightly in VSD patients, especially in those patients with CHF, in spite of the marked increase in their plasma hANP level. These results indicate that the capacity for hANP secretion was increased in VSD patients who had chronic volume overloading of the left atrium, but that their diuresis and urinary electrolyte excretion in response to hANP were attenuated.