Albert Einstein's cause of death was an abdominal aortic aneurysm, which ultimately led to his demise on April 18, 1955, at the age of 76.

An abdominal aortic aneurysm occurs when the wall of the aorta, the largest artery in the body, weakens and bulges outward. This condition is often asymptomatic until it reaches a critical size or ruptures, leading to severe internal bleeding.

In Einstein's case, the aneurysm was discovered in 1948 during a routine examination. At that time, surgery was considered a risky procedure, and doctors chose to monitor the aneurysm rather than operate.

Unfortunately, on April 12, 1955, Einstein experienced severe abdominal pain and was rushed to the hospital. The aneurysm had ruptured, causing massive internal bleeding. Despite undergoing surgery to repair the aneurysm, his condition deteriorated rapidly.

Einstein's health continued to decline, and he eventually fell into a coma. He passed away six days later, on April 18, 1955.

It's worth noting that Einstein's autopsy revealed additional health issues, including an enlarged heart and signs of renal artery stenosis, a narrowing of the arteries that supply blood to the kidneys. These conditions may have contributed to his overall health decline.

References:

1. Hansson K, et al. Albert Einstein's Aortic Aneurysm Surgery. Circulation. 2006;114(3):e74-e75.
2. Sautter RD, et al. Albert Einstein's heart: a medical analysis. Am J Cardiol. 2006;97(7):1053-1059.
3. Bogen JE. Albert Einstein and renal artery stenosis. JAMA. 1975;233(11):1185-1186.