The viability of the heart from irreversibly shocked dogs was evaluated. Thirty-one mongrel dogs were used to develop a uniformly lethal hemorrhagic shock model. The final model utilized a 30 mm. Hg mean arterial pressure with a 40 percent decompensation (uptake of reservoir blood). All control dogs subjected to this procedure died within 24 hours. Eleven hearts were transplanted following the shock procedure. Blood samples were drawn at intervals and analyzed for Po2, pH, glucose, oxygen content, and hematocrit. Cardiac outputs and ECG's were taken before and after transplant. All parameters measured returned to control levels following the transplants. Of the dogs receiving heart transplants, 10 survived more than 24 hours and eight survived more than 7 days. Compared with the survival of the shock model experiments, the survival of the transplant recipients was significant at the p less than 0.01 level. These results suggest that deterioration of the heart is not the factor which prevents recovery from irreversible hemorrhagic shock.