What is a stress myocardial perfusion scan?

A myocardial perfusion scan or MPS is a type of nuclear medicine procedure which means that a tiny amount of a radioactive substance, called a radionuclide (radiopharmaceutical or radioactive tracer), is used during the procedure to assist in the examination of the tissue under study. The myocardial perfusion scan evaluates the heart’s function and blood flow.
A radionuclide is a radioactive substance used as a "tracer". This tracer travels through the blood stream and is absorbed) by the healthy heart muscle tissue. During the scanning the regions where the radionuclide has been absorbed will show up differently than the areas that do not absorb it (due to decreased blood flow to the area or possible damage to the tissue from decreased or blocked blood flow).
A stress myocardial perfusion scan is used to assess the blood flow to the heart muscle or myocardium when it is stressed by exercise or medication and to determine what areas of the myocardium have decreased blood flow. This process is conducted by injecting a radionuclide (thallium or technetium) into a vein in the arm or hand.