When physicians recommend a stress test, they are usually referring to an exercise electrocardiogram (EKG). This test measures the heart's electrical activity before, during and after exercise. However, technically speaking, a stress test is any test that is performed in conjunction with exercise. Thus, a nuclear stress test usually refers to stress testing that is performed in combination with a nuclear imaging test, such as SPECT scan or a PET scan.

In general, a nuclear stress test is more accurate and provides more information than a standard exercise EKG. However, these tests do have drawbacks. They are more expensive and require more time, and there is exposure to a small amount of radioactive substances.

Because of cost issues and availability of radioactive tracers, the SPECT stress test is the more common of the two. During a SPECT stress test, the patient is injected with a very small, (of negligible harm) amount of a radioactive (radionuclide) substance, such as thallium.

Once in the patient’s body and taken by the heart, this substance emits rays that can be detected by a special gamma camera. The rays allow the camera to produce clear pictures of heart tissue on a video monitor. These pictures show contrasts between light and dark spots, which can indicate areas of damage or reduced blood flow that are present before, during and after exertion.

During a PET stress test, the radioactive tracer (usually rubidium-82) is attached to a molecule such as glucose. When the glucose is absorbed into the heart tissue, special sensors detect the rate of absorption and the degree of absorption. This allows physicians to evaluate the metabolic health of the tissue.

A nuclear stress test is often performed in addition to the procedures that come as a part of a standard stress test. Aside from some possible discomfort as the radionuclide substance is injected (twice), this is a painless test. Patients are generally asked not to eat or drink anything for four to six hours before the test, and to wear comfortable clothes and shoes for exercising. The time needed for the test will vary because different facilities use slightly different strategies for taking pictures of the heart at rest and during some form of exercise. Patients are encouraged to speak with their physician about the length of the test and any preparatory instructions. After the test, they can immediately return to their usual daily activities.

Depending on the results of  the nuclear stress test, the physician is often able to make a diagnosis and treatment plan for the patient. Further testing or procedures may need to be done.