Changes in plasma levels of atrial natriuretic peptide (ANP) and arginine vasopressin were studied in 5 patients during and after a 30-minute period of induced supraventricular tachycardia (SVT). Immediately after the induction of SVT, plasma ANP levels began to increase, peaked at 32 minutes (+734% increase on average) and then gradually decreased. The mean plasma arginine vasopressin levels decreased during SVT, but the differences were not significant. When plasma ANP levels during SVT were compared with the simultaneously measured hemodynamic variables, a significant positive correlation (r = 0.73, p less than 0.001) was observed between plasma ANP levels and pulmonary capillary wedge pressure. Induced SVT was associated with increased urinary sodium and potassium excretion, increased urine flow and increased free water clearance. Concomitantly, glomerular filtration rate significantly increased (+77%) with an increase in filtration fraction. Although no significant change was observed in plasma renin activity, plasma aldosterone concentrations decreased during and after SVT. These results suggest that increased left atrial pressure stimulates ANP release during SVT and that increased glomerular filtration rate and decreased aldosterone secretion by ANP, in addition to the inhibition of water reabsorption by decreased arginine vasopressin, may be responsible for natriuresis and diuresis associated with SVT.