The diagnosis of heart attack is based on three findings: characteristics of chest pain, ECG and blood test. If two of the three findings are present, it will confirm the diagnosis of heart attack. ECG is the most useful test as it usually shows characteristic changes within minutes of heart attack.

The eventual confirmation of heart attack is the blood tests, which detect proteins released into the blood stream when part of the heart muscle dies. However, these proteins (cardiac enzymes) can only be detected four to six hours after heart attack, which may be too late to implement treatment if treatment of heart attack is based on this alone.