Multigated acquisition (MUGA) scan can show how well your heart pumps blood. Ejection fraction (EF) is the percentage that the device measures. Your heart's ejection fraction (EF) measures how much blood it pumps out with each contraction. A MUGA scan produces a video of the heart's lower chambers, or ventricles, pumping blood. This reveals whether the heart's pumping action and blood flow are problematic. Before beginning cancer treatment, a MUGA scan is frequently performed. Before you receive therapy, this enables your medical team to better understand how your heart works.