This is a type of nuclear scanning test or myocardial perfusion (mi"o-KAR'de-al per-FU'zhun) imaging test. It shows how well blood flows to the heart muscle. It's usually done along with an exercise stress test on a treadmill.

The nuclear stress test is useful to determine:

• Extent of a coronary artery blockage
• Prognosis of patients who've suffered a heart attack
• Effectiveness of cardiac procedures done to improve circulation in coronary arteries
• Cause(s) of chest pain
• Level of exercise that a patient can safely perform

When the patient reaches his or her maximum level of exercise, a small amount of a radioactive substance (myoview or sestamibi) will be injected into the bloodstream. Then the patient lies down on a special table under a camera ("gamma camera") that can see the radioactive material and make pictures. The radioactive substance mixes with the blood in the bloodstream and heart's arteries and enters heart muscle cells. If a part of the heart muscle doesn't receive a normal blood supply, less than a normal amount of radioactive material will be in those heart muscle cells.

The first pictures are usually made at rest. The patient then waits for a some time and undergoes the stress portion of the test. The heart is "stressed" during the exercise test — thus the name "stress test." Another series of pictures is made. These show blood flow to the heart muscle after exercise.

What does the nuclear stress test show?

• If the test is normal during both exercise and rest, then blood flow through the coronary arteries is normal. The coronary arteries supply blood to the heart muscle.
• If the test shows that perfusion (blood flow) is normal during rest but not during exercise (a perfusion defect), then the heart isn't getting enough blood when it must work harder than normal. This may be due to a blockage in one or more coronary arteries.
• If the test is abnormal during both exercise and rest, there's limited blood flow to that part of the heart at all times.
• If no radioactive material is seen in some part of the heart muscle, the cells in this part of the heart are dead from a prior heart attack. (They have become scar tissue.)

What if I can't perform an exercise test?

Sometimes you can't do an exercise test because you're too sick or have physical problems. In this case, a drug such as adenosine is given. This drug increases blood flow to the heart and thus "mimics" an exercise test. Then the nuclear test is given.