Topic Overview

Heart failure with reduced ejection fraction (HFrEF) happens when the left side of your heart doesn't pump blood out to the body as well as normal.

It's sometimes called systolic heart failure. This is because your left ventricle doesn't squeeze forcefully enough during systole, which is the phase of your heartbeat when your heart pumps blood.

What does reduced ejection fraction mean?

The types of heart failure are based on a measurement called the ejection fraction. The ejection fraction measures how much blood inside the ventricle is pumped out with each contraction. The left ventricle squeezes and pumps some (but not all) of the blood in the ventricle out to your body. A normal ejection fraction is more than 55%. This means that 55% of the total blood in the left ventricle is pumped out with each heartbeat.

Heart failure with reduced ejection fraction happens when the muscle of the left ventricle is not pumping as well as normal. The ejection fraction is 40% or less.^{footnote 1}

The amount of blood being pumped out of the heart is less than the body needs. A reduced ejection fraction can happen because the left ventricle is enlarged and cannot pump normally.

Examples of ejection fractions of a healthy heart and a heart with reduced ejection fraction:

• A healthy heart with a total blood volume of 100 mL that pumps 60 mL has an ejection fraction of 60%.
• A heart with an enlarged left ventricle that has a total blood volume of 140 mL and pumps 60 mL has an ejection fraction of 43%.

What causes it?

There are many different problems that can cause heart failure with reduced ejection fraction.

Gradual heart damage

Coronary artery disease causes gradual heart damage over time. Ischemia is the medical term for what happens when your heart muscle doesn't get enough oxygen. Ischemia may happen only once in a while, such as when you are exercising and your heart muscle needs more oxygen than it normally does. Ischemia can also be ongoing (chronic) if your coronary arteries are so narrowed that they limit blood flow to your heart all the time. This chronic lack of oxygen can gradually damage portions of your heart muscle. Your heart can slowly lose its ability to pump blood to your body.

Chronic ischemia can allow your heart muscle to get just enough oxygen to stay alive but not enough oxygen to work normally. Ongoing poor blood flow to the heart muscle reduces the heart's ability to contract and causes it to pump less blood during each beat. The less blood your heart pumps out to your body, the less blood it is actually pumping back to itself through the coronary arteries. The end result is that heart failure makes ischemia worse, which in turn makes heart failure worse.

Mitral valve regurgitation can gradually lead to heart failure. With this problem, the mitral valve doesn't close properly, and blood leaks back into the left atrium when the left ventricle contracts. Over time, the left ventricle pumps harder to move the extra blood that has returned to it from the left atrium. The ventricle stretches and gets bigger to hold the larger volume of blood. Gradual weakening of the left ventricle may cause heart failure.

High blood pressure can also gradually lead to heart failure. To pump against your high blood pressure, your heart has to increase the pressure inside your left ventricle when it pumps. After years of working harder to pump blood, your ventricle may begin to weaken. When this happens, the pressure inside the weakened left ventricle will cause the ventricle to expand, stretching out the heart muscle. This damaging process is called dilation, and it impairs your heart's ability to squeeze forcefully. The result is heart failure.

Sudden heart damage

A heart attack damages heart muscle suddenly. A heart attack can cut off the flow of blood to your heart muscle so that your heart muscle doesn't get any oxygen. If your heart muscle goes without oxygen for long enough, heart muscle can die. If a heart attack damages a very large area of heart muscle, it is possible that the ability of your heart to pump blood will be suddenly limited to such a degree that you develop heart failure. But this sudden complication isn't common.

If you have a substantial heart attack that injures a large area of the heart muscle, you may eventually develop heart failure, even if it doesn't occur suddenly. This happens most commonly after you have had a heart attack involving the anterior wall of the heart. After a large area of the anterior wall is destroyed, the percentage of blood pumped with each beat (ejection fraction) can be significantly less. As a result, the heart attempts to change its shape to maximize its pumping efficiency, a process referred to as left ventricular remodelling. Initially, the changes made to the heart wall (myocardium) are beneficial. Over time though, the left ventricle dilates and increases in size, which makes the heart less able to pump.