Ejection fraction (EF) is a measurement of how much blood your heart pushes out when it beats. This measurement helps with the diagnosis and treatment of heart failure.
Your heart has 4 chambers. The top 2, called the atria, take blood in from the veins and lungs. The bottom 2 are called ventricles. When your heart beats, the right ventricle pumps blood to your lungs and the left ventricle pumps blood to the rest of your body. The EF is the percentage of blood that is pumped out of a ventricle with each heartbeat. Even in a healthy heart, some blood stays behind in the ventricles.
EFs between 55% and 75% are considered normal for the left ventricle, which is the main pumping chamber of the heart. In heart failure caused by a weak heart muscle, the EF number can become very small. An EF of 20% means 80% of the blood stays in the ventricle and therefore the heart is not providing all the blood the body needs.
Doctors can use an echocardiogram, or other techniques, such as cardiac MRI, cardiac catheterization, or nuclear imaging, to measure EF and see how well your heart is working.
Although the EF is very important and is one of the most commonly used method of expressing overall heart function, it is important to note that some people have heart failure symptoms despite a normal-range EF. Also, although a low EF is never normal, with treatment some people can lead a fairly normal, active life despite a decreased EF.