The effects of atrial natriuretic peptide (ANP) infusion were determined in 9 subjects undergoing cardiac catheterization which did not disclose heart disease. Data were obtained at rest and during the steady-state phase of alpha-human-(1-28)-atrial natriuretic peptide infusion (0.5 microgram/Kg bolus dose, 0.05 microgram Kg/min iv for 20 min). Mean blood pressure decreased from 105 +/- 3 to 98 +/- 4 mmHg (p less than 0.05); pressure measurements and left ventricular (LV) angiograms suitable for analysis were available in 7 of 9 subjects at matched heart rate. The infusion of ANP reduced LV end-diastolic and end-systolic volume indices from 93 +/- 6 to 80 +/- 6 ml/m2 (p less than 0.01) and from 25 +/- 3 to 17 +/- 1 ml/m2 (p less than 0.05), respectively. Left ventricular ejection fraction insignificantly increased from 72 +/- 5 to 77 +/- 4%. End-systolic pressure/volume ratio showed a slight but not significant rise (from 3 +/- 0.4 to 4 +/- 0.8). Initial plasma levels of ANP (48 +/- 12 pg/ml) rose to 1890 +/- 423 pg/ml (p less than 0.001) during the infusion and individual hemodynamic responses were not related to plasma concentrations of the peptide. These data suggest that the administration of ANP has no negative effects on LV function and the ANP-induced changes on cardiac performance are related to the reduced cardiac load.