Test, radionucleide stress: This procedure involves injecting a radioactive isotope (typically thallium or cardiolyte) into the patient's vein after which an image of the patient's heart becomes visible with a special camera. The radioactive isotopes are absorbed by the normal heart muscle. Nuclear images are obtained in the resting condition, and again immediately following exercise. The two sets of images are then compared.
During exercise, if a blockage in a coronary artery results in diminished blood flow to a part of the cardiac muscle, this region of the heart will appear as a relative "cold spot" on the nuclear scan. This cold spot is not visible on the images that are taken while the patient is at rest (when coronary flow is adequate).