Background: A novel donor heart preservation solution was formulated to produce hyperpolarized arrest with the potassium channel opener, pinacidil. The superior cardioprotective efficacy of this solution has been demonstrated previously when compared to University of Wisconsin solution following 4 hours of hypothermic ischemia. This study tested the hypothesis that pinacidil solution may extend preservation time and provide superior cardioprotective efficacy following 12 hours of ischemia. Methods: Sixteen rabbit hearts were assigned to receive either pinacidil solution or University of Wisconsin solution in a crystalloid-perfused Langendorff model. Thirty minutes of initial perfusion preceded baseline data acquisition. Left ventricle pressure-volume curves were generated by inflating an intra-ventricular latex balloon. Following cardioplegic administration, hearts underwent 12 hours of hypothermic storage. After 60 minutes of reperfusion, post-ischemic data were acquired. Results: Pinacidil solution demonstrated significantly better myocardial preservation compared to University of Wisconsin solution, with better recovery of developed pressure (53.0±11.1% vs 20.7±4.3%, p=0.017, respectively), post-ischemic coronary flow (55.3±12.6% vs 23.9±4.3%, p=0.034), maximum systolic dP/dT (46.4±8.3% vs 20.2±5.1%, p=0.018) and minimum diastolic -dP/dT (65.3±10.8% vs 20.2±5.1%, p=0.002). Diastolic compliance, expressed as baseline/post-ischemic diastolic slope ratios, was also better preserved by pinacidil solution (0.55±0.09) vs University of Wisconsin solution (0.40±0.03) (p=0.135). Conclusions: A novel pinacidil solution resulted in improved donor heart preservation during 12 hours of hypothermic ischemia compared to the "gold standard," University of Wisconsin solution. Adopting alternative strategies of hyperpolarized arrest may allow extension of preservation time beyond the limits of traditional depolarizing solutions.