Sternal injury, gross cardiac pathology, and cardiac dysrhythmias following nonpenetrating impact by a variety of impactors to the sternum of experimental animals are described. The biomechanical response of the chest wall to the impact and the associated transient pressure changes within the heart are presented, and a correlation between injury severity and chest wall displacement is demonstrated. A simple model is then developed to predict chest wall displacement if the mass, velocity, and dimensions of an impactor are known. The model demonstrates the dependence of chest-wall displacement upon preimpact kinetic energy, impact diameter, and target size.