To evaluate the effects of synthetic human atrial natriuretic peptide (hANP) on myocardial reperfusion injury and left ventricular remodeling, 19 patients within 12 h of a first attack of anterior myocardial infarction (AMI) underwent intracoronary injection of 25 microg of hANP immediately after coronary angioplasty, combined with intravenous infusion of 0.025 microg x kg(-1) x min(-1) of hANP initiated on admission for 1 week (hANP group); 18 similar patients had saline administered (control group). The incidences of premature ventricular contraction, ventricular tachycardia and/or fibrillation in the hANP group were significantly less than in the control group after coronary angioplasty. Left ventricular ejection fraction was significantly greater and left ventricular end-diastolic volume index was significantly smaller 6 months after coronary angioplasty. Left ventricular regional wall motion of the infarcted segments significantly increased. Thus, hANP remarkably suppressed reperfusion phenomena and preserved left ventricular function through improvement of regional wall motion of the infarcted segments after coronary angioplasty.