To determine the efficacy of very low doses of adenosine on myocardial reperfusion injury and whether its effect is receptor mediated, 78 rabbits underwent 30 minutes of left circumflex artery occlusion and 48 hours of reperfusion. Animals were randomly assigned to receive one of three doses of adenosine, cyclopentyladenosine (a selective A1-receptor agonist), or CGS 21680C (a selective A2-receptor agonist). The drugs were infused for 65 minutes beginning 5 minutes before reperfusion. A significant reduction in histologically determined infarct size was noted with all three doses of adenosine, intermediate and low doses of the A1-receptor agonist (cyclopentyladenosine), and high and intermediate doses of the A2-receptor agonist (CGS 21680C). Furthermore, all three adenosine receptor agonists afforded similar degrees of protection. Results of this study demonstrate that intravenous infusions of very low doses of adenosine significantly enhance myocardial salvage and this protection is receptor mediated. Furthermore, the administration of the A1-receptor agonist would be clinically appealing, since it would avoid the potential side effects associated with activation of A2 receptors.