One possible reason for improved function of the left ventricle with beta-blockers is improved blood flow to the heart muscle. When a region of the heart is active, it uses more fuel in the form of oxygen and sugar (glucose). As heart activity increases, blood flow to and from the area of activity increases also. Knowing these facts, researchers can use radioactive sugar (glucose) and positron emission tomography (PET) scans to observe what areas of the heart are receiving more blood flow.