Furring up of the arteries (atheroma) develops over many years and can occur both suddenly and gradually:

Gradual progression of the furring up process typically causes angina; however, another manifestation of the same disease process is a myocardial infarction. In the majority of cases an area of atheroma suddenly ruptures, exposing the undersurface of the artery lining and provoking an injury response, whereby a clot begins to form over the damaged area. If the clot is large enough it can block the artery entirely and this is the substrate for a heart attack.

In most cases this is unheralded and is often the first indication that a patient has a heart problem, hence the importance of screening in medium and high risk populations. Sometimes a patient will have had angina symptoms which suddenly intensify such that chest discomfort develops with diminishing levels of exercise and is ultimately present at rest.

Most survivors describe a heart attack as an intense discomfort and heaviness in the chest, like an elephant sitting on the chest, associated with sweating, nausea and breathlessness. This is a medical emergency and needs immediate treatment, known as primary angioplasty, where a stent is inserted to unblock the artery, to restore the blood supply to the heart and minimise damage to the heart muscle. During a heart attack, the heart muscle that received its blood supply from the affected artery will die, healing with time to leave a scar. The larger the scar, the greater the effect on the remaining healthy heart muscle, and the less effectively the heart will work in the future.