Background: The University of Wisconsin (UW) solution is the gold standard for heart preservation but has limitations in terms of both duration and adequacy of protection. Our laboratory has been interested in a more physiologic approach to heart preservation by maintaining the heart at its resting membrane potential (hyperpolarized arrest) with the KATP channel agonist pinacidil. This study compared our extracellular solution (WashU) with the UW intracellular depolarizing solution and quantified the protective effect of pinacidil in both solutions. Methods: Thirty-two rabbit hearts received 1 of 4 solutions in a crystalloid-perfused Langendorff apparatus: (1) UW, (2) WashU containing 0.5 mmol/liter pinacidil, (3) UW with 0.5 mmol/liter pinacidil, or (4) WashU without pinacidil. Thirty minutes of perfusion was followed by data acquisition consisting of left ventricular pressure-volume curves generated by inflating an intraventricular balloon. All hearts were placed in cold storage for 8 hours, followed by 1 hour of reperfusion before data acquisition. Results: Post-ischemic developed pressure (DP) was better preserved by WashU (76.8% ± 3.8%) than by UW (48.3% ± 2.5%). Diastolic compliance was better preserved by WashU (239.9% ± 77.2%) compared with UW (711.1% ± 193.1%). Removing pinacidil from our solution resulted in decreased DP (46.6% ± 3.2%) and diastolic compliance (688.8% ± 158.2%) Adding pinacidil to UW had a limited effect on DP and compliance. Conclusions: Our results support the superiority of the WashU hyperpolarizing solution for heart preservation over UW. Pinacidil was beneficial in maintaining cardiac function and compliance. This benefit was not observed when pinacidil was placed into the UW depolarizing solution.