One way in which a physician diagnoses coronary heart disease is through nuclear imaging. During nuclear imaging, a small dose of a radioactive isotope is injected into the bloodstream. The radioisotope, or tracer, is carried through the bloodstream and into the myocardium, or heart muscle. Special cameras detect the radiation released from the tracers and record information about the heart muscle and blood flow. This information is then used to produce images of the heart on a computer screen or film.