Thoracic impact response and injuries of living and postmortem porcine siblings were investigated to quantify comparative differences. Thirteen male animals, averaging 61.4 kg, from five different porcine litters comprised the two animal samples. Porcine brothers were subjected to similar impact exposures for which at least one brother was tested live, anesthetized and another dead, post rigor with vascular repressurization.Statistically significant differences in biomechanical responses and injuries were observed between live and postmortem siblings. On the average the anesthetized live animals demonstrated a greater thoracic compliance, as measured by increased normalized total deflections (21% Hi), and reduced overall injuries (AIS 14% Lo and rib fractures 26% Lo) at lower peak force levels (13% Lo) than did the postmortem subjects. However, individual comparisons of “match-tested” siblings demonstrated very similar responses in some cases. The living animals developed myocardial conductive system dysfunctions encompassing arrythmias, blocks and ventricular fibrillation which were poorly correlated to gross autopsy findings of heart trauma and the overall AIS. Arterial overpressures were substantially higher (three times) in the postmortem animals indicating that the experimental protocol produced an unrealistic arterial system impact response.A procedure is suggested which uses the live versus postmortem animal response and injury data to revise an existing injury versus normalized deflection relationship based upon human cadaver data.