Simplified schematic illustrates experimental protocol. Isolated rat hearts were subjected to 15 minutes of equilibration, followed by 25 minutes of warm ischemia (37°C) and then 40 minutes of reperfusion. During reperfusion period, either perfusate, PPT (1 nM, 10 nM, or 100 nM), or DPN (1 nM, 10 nM, or 100 nM) is infused.