Losartan, an angiotensin II receptor antagonist with no bradykinin potentiating property, provides the opportunity to study the consequences of blocking angiotensin II. The objective of this study was to evaluate the antiarrhythmic responses of reperfusion arrhythmia to losartan in dogs. The effects of losartan on ventricular tachyarrhythmias induced during occlusion and reperfusion of the left anterior descending coronary artery were investigated in 30 dogs. The animals were randomized to receive either losartan (n = 15) or saline (n = 15). The VF inducing threshold was measured before occlusion and after reperfusion. Losartan (50 micrograms/kg per min) or saline was intravenously administered 5 minutes before occlusion and continued throughout the entire study period. The incidence of ventricular tachyarrhythmias during reperfusion was lower in the losartan group than in the control group (4/15 vs 6/15). There was no significant change in VF inducing threshold between the period before occlusion and during reperfusion in the losartan group [10.9 +/- 5.7 vs 11.1 +/- 5.7 mA, P = NS), whereas there was a significant decrease in the control group (15.5 +/- 4.4 vs 7.7 +/- 3.9 mA, P < 0.01). Blockade of the angiotensin II receptor has beneficial effects on reperfusion arrhythmias.