An embolism was an obstruction in a blood vessel due to a blood clot or other foreign matter that became stuck while traveling through the bloodstream. In 1994, Clare Raymond died of a massive embolism,. As her husband Donald had her body frozen and stored in a cryonics satellite, she was able to be revived about 374 years later. When Doctor Beverly Crusher told her how she'd died, she confessed that she knew nothing about having passed away. (TNG: "The Neutral Zone" )