An aneurysm is an abnormal dilatation of an artery, often as a result of atherosclerotic disease. Hypertension, connective-tissue disease and a family history of aneurysms are predisposing risk factors. They may occur at any point in the vasculature from the aortic root to distal peripheral vessels, but they are most common in the abdominal aorta. Many times they are asymptomatic and undiagnosed, but as they progressively enlarge, they may compress on surrounding structures, release atherosclerotic debris or thrombi and possibly rupture. Aneurysms occur in approximately 3% of people older than 50; some of these do not rupture. An aneurysm is not typically painful until it dissects or ruptures. [table: see text] The abdominal aorta splits at the level of the umbilicus, so the abdomen must be palpated above the level of the umbilicus to feel for aortic enlargement. Obese patients make detection more difficult, as the presence of a pulsatile mass may be covered. An aneurysm will still conduct blood flow into the lower extremities, so pulses will not be compromised, and capillary refill and temperature will be normal. An acute rupture is a catastrophic event characterized by poor perfusion or frank shock and pain in the abdomen, back or groin. Accompanying symptoms may include a pulsatile abdominal mass, absence of distal pulses, and radiating pain into the lower back that is often described as "tearing" or "ripping." The risk of rupture has a direct correlation with an aneurysm's size. Generally, elective surgery is considered with an abdominal aneurysm larger than 4.5 centimeters, but there are many factors which may preclude repair. Non-surgical treatment of an aneurysm has been performed by percutaneously placing a prosthetic graft at the site, anchoring the graft above and below the aneurysm, thereby isolating the aneurysm from the circulation. Surgical treatment for elective repair of an aneurysm that is not ruptured is still very difficult and has a significant risk of complications. A ruptured abdominal aortic aneurysm has a very high incidence of mortality. Early identification and rapid transport to a facility with vascular surgery services are the keys to survival. This case demonstrates early recognition by the EMS crew and successful resuscitation from a cardiac arrest due to profound shock. In other cases, EMS providers may have the first and only opportunity to recognize a ruptured aneurysm and direct the ED and surgical teams to the cause of sudden shock or cardiac arrest.