Marfan's is a genetic disease that results in an abnormal protein fibrillin, and leads to weakening of structures like the lenses in the eye. More importantly, it can lead to a bicuspid aortic valve in the heart (instead of three valve leaflets there are only two). It can also lead to weakening of the aorta. The valve issues can cause narrowing, leakage, and poor performance. The weakening of the aorta can lead to an aortic dissection, where the layers of the aorta can delaminate and block blood flow to the head, coronary arteries, etc.
The only treatment for this is surgical, replacement of the aortic root with a graft, and replacement of the aortic valve with either a pig valve, a cow valve, or a mechanical valve. Without this surgery, a person with Marfan's is at risk for sudden death due to aortic dissection. Unfortunately, this sounds like the situation here.