With a Heart Attack, people usually die from this because of one of two processes. One way that seems to get all the attention is the blocked arteries that choke off the blood supply and causes blockage with or without heart muscle damage.
The other process is called "rupture of vulnerable plaque". There is a lot of study going on about this subject. A simple way of thinking about this is visualize a pimple sitting on the inside of an artery. As long as that pimple doesn't break open then there is no emergency. But, if that pimple breaks open and material leaks out it violently interacts biologically with blood and forms clots that can kill.
"The clots then pass through and always seem to end up in an inconvenient place like plugging an arterial branch in the heart, the lungs creating a pulmonary clot (embolisms) and the leg area, for example. Inconvenient in this case means a cessation of critical blood flow resulting in death. Fully 50% of the time when folks are falling to the floor with crushing pain or sensing something terribly wrong and dying, they are learning for the first time the hard way that they have coronary heart disease."
Heart disease is the USA leading cause of death. Much of the burden of heart disease could be eliminated by reducing the prevalence rates of its major risk factors: high blood pressure, high blood cholesterol, tobacco use, diabetes, physical inactivity, and poor nutrition. Modest reductions in the rates of one or more of these risk factors can have a large public health impact.
And....YOU COULD AVOID AN EARLY DEATH.
Heart disease, which killed more than 700,000 Americans in 2001, accounted for 29% of all deaths in the United States. In 2001, the rate of death from heart disease was 31% higher among blacks than whites and 49% higher among men than women. In 2001, heart disease cost the nation $193.8 billion. About 66% of heart attack patients do not make a complete recovery.