Also known as radionuclide/nuclear ventriculography or radionuclide angiography, a multiple-gated acquisition (MUGA) test uses radioactive substance o track how blood flows through your heart while you’re resting or moving. In this test, your doctor will put sticky pads called electrodes on your chest, which will record your heart’s electrical activity. Then a radioactive material, called a tracer, will be injected into a vein in your arm. The tracer binds to your red blood cells, which carry oxygen throughout your body. A special camera above your chest will take pictures from various angles, which will track the tracer as it moves through your bloodstream. You may be asked to exercise in between pictures to help your doctor see how your heart responds to activity. The entire test may take up to 3 hours to finish.