Blunt trauma to the thorax produces a variety of injuries, but death is frequently related to arterial bleeding without other major organ damage. This paper is concerned only with injuries to the arterial system of the chest after experiencing sternal impact designed to simulate the injury of many automotive or airplane crashes. Strassman, in 1947, called attention to the fact that thoracic great vessel injury is a frequent cause of death when pedestrians are struck by cars and when a driver impacts a steering wheel assembly. Because accidents of this type are most dramatically evident during deceleration without driver restraint, this type of injury has been thought of as a deceleration injury. Tears of the thoracic vascular system, however, are not a sole product of the Machine Age and high speed transportation, since Vesalius, in 1557 (Roth, 1892), recorded a case where a man was thrown from a horse and apparently developed a traumatic thoracic aneurysm. This series of experiments was undertaken in an effort to determine the mechanism producing the tears which have been reported in the aorta and great vessels, and also to determine what parameters could be quantitated which might be responsible for he consistent pattern of injury which has been reported (Hass, 1944). Therefore, acute and chronic studies of dogs exposed to non-penetrating blunt trauma to the thorax were undertaken.