To examine the role of oxygen free radicals and extracellular calcium ions in reperfusion-induced ventricular arrhythmias, we evaluated the effects of hypoxic reperfusion, oxygen free radical scavengers, allopurinol and hypocalcemic reperfusion on reperfusion-induced ventricular arrhythmias. The hearts of male Sprague-Dawley rats were perfused in the working heart mode. Whole heart ischemia was induced for 15 min and then reperfused. Rats were divided into 5 groups: control group, scavenger group, allopurinol group, hypoxia group and hypocalcemia group. Scavenger, hypoxic and hypocalcemic perfusions were undertaken only during the period of perfusion. The incidence of reperfusion-induced ventricular fibrillation (Vf) was reduced in the scavenger group (100% to 38%) and the hypoxia group (100% to 50%). Spontaneous reversion of Vf to regular sinus rhythm was recognized in the hypoxia and hypocalcemia groups. In conclusion, oxygen free radicals would play an important role in the genesis of the reperfusion arrhythmias, and extracellular calcium concentration would also play an important role in sustaining the reperfusion arrhythmias. Notably, hypoxic reperfusion had protective effects on both processes.