Weakened heart muscle can reduce the amount of blood it pumps. A common cause of weakened heart
muscle is a single, large heart
attack or repeated smaller heart
attacks (a heart attack doesn't always have symptoms) . Also, conditions that can weaken the ability of the heart to pump blood include medications that are toxic to the heart, infections of the muscle of the heart by viruses and diseases of the heart's valves such as aortic stenosis.