We investigated the effects of pressure, temperature and additives on aortic root reperfusion success. Cardiopulmonary bypass and heart arrest were initiated in mongrel dogs and sudden uncontrolled normothermic (group 1), pressure controlled substrate enriched normothermic (group 2a), pressure controlled unmodified normothermic (group 2b) and pressure controlled unmodified tepid (group 3) reperfusion compared. In group 1, the first cardiac rhythm was ventricular fibrillation, but dogs in the other groups showed spontaneous sinus rhythm. Recovery times were significantly longer and cardiac output levels significantly decreased in group 1 compared with the other groups. Prolonged lactate production and oxygen uptake failure were observed in group 1 compared with the other groups; oxidative stress markers and microscopic studies confirmed significant tissue injury in group 1. All parameters were similar between groups 2a, 2b and 3, indicating that low reperfusion pressure in the first 2 min is the most effective component of reperfusion.