OBJECTIVE: The dynamic response of the heart during chest impact and the characteristics of heart injuries were investigated to further understand the mechanisms of heart impact injuries. METHODS: Eleven dogs and thirty-four rabbits were subjected to front thoracic impact with different impact velocities and compression response. The accelerated movement of thoracic wall during the impact period was monitored. The pathological examination of the injured heart was done and the dynamic responses and mechanisms of injuries were analyzed with mathematics models. RESULTS: The analysis of mathematics model and experimental results showed that the injury severity of heart was well correlated with the viscous criterion. The thoracic wall was involved in bi-directional movement of compression and expansion. The injured heart showed spotty or stripy hemorrhages in the ventricle endocardium. Light microscopic examination showed interstitial bleeding and rupture of the myocardial fibers in the contusion area. The biomechanical analysis indicated that there was a large deformation caused by the stress concentration on the lateral ventricle wall. CONCLUSIONS: There is a high speed and excessive deformation of the heart during the impact period, which might be the key mechanism of heart injury. The strong impact and press coming from both sternum and vertebral column and the rapid elevation of pressure in the ventricle are the main cause of deformation.