Recent advances in novel medical gases, including hydrogen and carbon monoxide (CO), have demonstrated significant opportunities for therapeutic use. This study was designed to evaluate the effects of inhaled hydrogen or CO, or both, on cold ischemia/reperfusion (I/R) injury of the myocardium. Syngeneic heterotopic heart transplantation was performed in rats after 6 or 18 hours of cold ischemia in Celsior …