A diagnosis of heart attack needs to be confirmed immediately. Tests to confirm the occurrence of a heart attack are sometimes conducted by emergency medical personnel in an ambulance. Other tests are done at the hospital immediately after the patient arrives.

One frequently used test is an electrocardiogram, also called an ECG or EKG. This is a graphic record of the electrical activity of the heart. The ECG can detect abnormal heart rhythms, areas of heart damage, and heart enlargement.

A blood test is conducted routinely to check for evidence that cells in the heart have begun to die. This blood test detects the release of muscle enzymes, such as troponin, creatinine kinase, and other substances. These substances may signal damage to the heart, and help determine the amount of damage that has occurred.

An echocardiogram, a study using reflected sound waves to create an image of the heart, is often performed to assess how much damage has occurred from a heart attack. The provider can also view the heart valves and the heart lining.

Another type of test that can be used to diagnose heart attack is called a nuclear scan, for example a thallium stress test. This test can reveal areas of the heart that lack blood flow and are damaged. A small amount of radioactive material is injected into a vein, usually in the arm. A scanning camera positioned over the heart records whether the nuclear material is taken up by the healthy areas of heart muscle, or not taken up by damaged areas. This test can also help evaluate how well the heart muscle pumps blood.

Coronary angiography, sometimes called arteriography, is a test used to check blockages and narrowed areas inside coronary arteries. A thin, flexible tube, called a catheter, is threaded through an artery of an arm or leg up into the heart. Contrast material, or dye that shows up on X-ray, is then injected into the blood vessel, and the vessels and heart are filmed. The picture is called an angiogram or arteriogram, and indicates exactly where the coronary artery is blocked.