US Sen. Lindsey Graham, a Republican from South Carolina, died on Saturday night from a tear in his artery, according to preliminary findings from a medical examiner.

Aortic dissection is rare, and life-threatening in most cases, experts say. The acute event happens quickly but there are steps you can take to lower your risk.

The aorta is the largest blood vessel in body and the first place blood travels through as it’s pumped from the heart to other parts of the body.

An aortic dissection occurs when there is a tear in the aorta, which disrupts the critical source of blood flow.

Dr. Barbara Hamilton, an assistant professor of cardiac surgery with a specialty in aortic surgery at the University of Michigan, says the aorta is like an onion with many layers. A tear can happen on the inner layer of the aorta, which would create a “false passage” for blood, she said — letting it travel between the layers of the blood vessel instead of reaching important organs.