Causes

Heart failure often develops after other conditions have damaged or weakened the heart. However, heart failure can also occur if the heart becomes too stiff.

In heart failure, the main pumping chambers of the heart (the ventricles) may become stiff and not fill properly between beats. In some people, the heart muscle may become damaged and weakened. The ventricles may stretch to the point that the heart can't pump enough blood through the body.

Over time, the heart can no longer keep up with the typical demands placed on it to pump blood to the rest of the body.

Your doctor can determine how well your heart is pumping by measuring how much blood is pumped out with each beat (ejection fraction). Ejection fraction is used to help classify heart failure and guide treatment. In a healthy heart, the ejection fraction is 50% or higher — meaning that more than half of the blood that fills the ventricle is pumped out with each beat.

But heart failure can occur even with a normal ejection fraction. This happens if the heart muscle becomes stiff from conditions such as high blood pressure.

Heart failure can involve the left side (left ventricle), right side (right ventricle) or both sides of your heart. Generally, heart failure begins with the left side, specifically the left ventricle — your heart's main pumping chamber.

Any of the following conditions can damage or weaken your heart and can cause heart failure. Some of these can be present without your knowing it:

• Coronary artery disease and heart attack. Coronary artery disease is the most common form of heart disease and the most common cause of heart failure. The disease results from the buildup of fatty deposits in the arteries, which reduces blood flow and can lead to heart attack.

  A heart attack occurs suddenly when a coronary artery becomes completely blocked. Damage to your heart muscle from a heart attack may mean that your heart can no longer pump as well as it should.

• High blood pressure. If your blood pressure is high, your heart has to work harder than it should to circulate blood throughout your body. Over time, this extra exertion can make your heart muscle too stiff or too weak to properly pump blood.
• Faulty heart valves. The valves of the heart keep blood flowing in the proper direction. A damaged valve — due to a heart defect, coronary artery disease or heart infection — forces the heart to work harder, which can weaken it over time.
• Damage to the heart muscle. Heart muscle damage can have many causes, including certain diseases, infection, heavy alcohol use, and the toxic effect of drugs, such as cocaine or some drugs used for chemotherapy. Genetic factors also can play a role.
• Inflammation of the heart muscle (myocarditis). Myocarditis is most commonly caused by a virus, including the COVID-19 virus, and can lead to left-sided heart failure.
• A heart problem that you're born with (congenital heart defect). If your heart and its chambers or valves haven't formed correctly, the healthy parts of your heart have to work harder to pump blood, which may lead to heart failure.
• Abnormal heart rhythms (arrhythmias). Abnormal heart rhythms may cause your heart to beat too fast, creating extra work for your heart. A slow heartbeat also may lead to heart failure.
• Other diseases. Long-term diseases — such as diabetes, HIV, an overactive or underactive thyroid, or a buildup of iron or protein — also may contribute to chronic heart failure.

Causes of sudden (acute) heart failure also include:

• Allergic reactions
• Any illness that affects the whole body
• Blood clots in the lungs
• Severe infections
• Use of certain medications
• Viruses that attack the heart muscle