It bursts. The wall of the aorta tears because of increased pressure from the expanding aneurysm. Ruptures can be "contained, " with the bleeding confined by the lining of the abdominal cavity, or they can be "free ruptures, " when the bleeding occurs into the abdominal cavity. The second type is more deadly. Mortality with ruptured aneurysms is 50-90%. As many as 50% of people die before reaching the hospital.
Bleeding. The biggest "pipe" in the body is the aorta. It carries blood in it. When this pipe breaks, there will be massive bleeding leading to shock that maybe a precursor for heart attack, stroke or kidney failure. Depending upon size and location , open surgical or minimally invasive endovascular stent maybe needed. Please see a vascular surgeon.