The emergency department thoracotomy (EDT) is a bold and challenging procedure, which may be the only chance of survival for some moribund trauma patients. EDT provides ample exposure to the injury site of the heart, enabling an effective open cardiac massage. Clamshell thoracotomy is a rapid and simple procedure that provides excellent exposure to internal structures. Because EDT has more favorable outcomes for penetrating injuries than for blunt injuries, the indication for EDT in patients with blunt trauma should be well established. Cardiac tamponade is a life-threatening condition that requires emergent pericardial decompression. EDT has been associated with successful initial resuscitation for traumatic cardiac arrest with cardiac tamponade. To date, there has not been any reports of clamshell incision via EDT for trauma patients in South Korea. Hence, herein, we describe two cases in which EDT with clamshell incision was implemented for cardiac tamponade with cardiac arrest after blunt trauma.