To understand heart ejection fraction, you first need to understand how your heart pumps your blood through your body. Most people think that the heart pumps out ALL the blood that comes into it; however, the reality is that your heart works more like a bucket used to bail out a boat. If you don’t turn the bucket upside down, then you’ll toss out most of the water, but not all, before you refill it.
Instead, some of it sloshes back to the “bottom of the bucket.” The same principle is true of your heart.
The blood moves through the four chambers of the heart, making a quick stop between the right side and the left side of the heart to pick up a fresh supply of oxygen in the lungs. The right and left atria (“atria” is plural for atrium) are “receiving chambers.”
The atria then pump blood out to the ventricles, which are the two larger, lower chambers that in turn pump blood out to the lungs and the aorta. Blood comes in from the largest veins in the body (the vena cava) to the right atrium, then down to the right ventricle, then out to the lungs for oxygen, back to the left atrium, down to the left ventricle, then out of the heart again to the aorta and the body.
So the path is: Vena Cava—Right Atrium—Right Ventricle—LUNGS—Left Atrium—Left Ventricle—AORTA.
Measuring Heart Ejection Fraction
Heart ejection fraction is used to evaluate the heart’s primary function as a pump. Heart ejection fraction is measured at the point where the left ventricle pumps blood out into the aorta. It can be calculated non-invasively with an echocardiogram or more directly during an angiogram of the heart. A non-invasive MUGAscan of the heart will also estimate the heart ejection fraction.
A healthy heart is able to eject, or “bail out”, about 50 to 70 percent of the blood that comes in. The person with a 50 to 70 percent heart ejection fraction feels great (from a cardiac standpoint anyway).
When the heart ejection fraction is less than 50 percent, their heart may have trouble keeping up with the oxygen demand of physical activity. Some may start to have symptoms at ejection fractions of 35 to 45 percent, but not always.
People with advancing heart failure—where the heart muscle has trouble moving blood in a forward fashion—have heart ejection fractions below 35 percent. Those awaiting heart transplants often have an even lower ejection fraction—often 10 to 15 percent—and it’s all they can do to sustain simple activity, such as getting from a bed to a chair.
One of the reasons for this is that a low heart ejection fraction results in blood backing up into the lungs, creating the breathing difficulties commonly experienced in someone with congestive heart failure. Other cardiovascular problems that can adversely affect ejection fraction include heart attack, long-standing high blood pressure levels, valvular issues, and infections of the heart muscle.