The heart is contained within the pericardial sac. Numerous portions of the heart are exposed behind the anterior chest wall (Figure 36-2). This includes the right ventricle, left ventricle, right atrium, left atrium, aorta, pulmonary artery, and inferior vena cava. These structures are vulnerable to injury behind the anterior chest wall.3,4 The surface areas that each of these structures contributes to the anterior cardiac silhouette are as follows: 55% right ventricle, 20% left ventricle, 10% right atrium, 10% aorta and pulmonary artery, 4% inferior vena cava, and 1% left atrium.5 These numbers also reflect, roughly, the anatomic incidence of injury with cardiac trauma.5 Traumatic injury to any of these structures can result in a pericardial effusion and cardiac tamponade.