The aortic tear that likely caused the sudden death of Sen. Lindsey Graham is a medical emergency that can rapidly kill. The aorta is our largest artery, like a highway that carries oxygen-rich blood to the rest of the body as other arteries branch off from it. What doctors call an aortic dissection happens when a tear in its inner lining lets blood rapidly leak between its other layers, reducing its flow to vital organs, or sometimes rupture, according to the American Heart Association.