Preservation of a donor heart for transplantation is limited to 6-8 hours. Based on our demonstration of 12 hour perfusion with plasma cross circulation, this study aimed to evaluate ex vivo heart perfusion (EVHP) for up to 72 hours using cross plasma circulation (XC-plasma) from a live, awake paracorporeal sheep (PCS). Six ovine hearts were perfused for 72 hours using plasma cross circulation at a rate of 1 L/min with a live, awake PCS. Controls were seven perfused hearts without cross circulation. Experiments were electively ended at 72 hours, and epinephrine (0.1 mg) was delivered to demonstrate hormonal responsiveness. All controls failed at 6-10 hours. All six hearts perfused for 72 hours maintained normal heart function, metabolism, and responsiveness to epinephrine. Blood gases, electrolytes, and lactate levels were normal and stable throughout the study. All hearts appeared suitable for transplantation. We have demonstrated successful normothermic EVHP for 72 hours.