An ejection fraction is a measurement that tells what percentage of blood is pumped out of a ventricle in the heart with each beat. It is usually measured from the left ventricle, which is the main pumping chamber in the heart. Sometimes it is qualified as the right ventricle ejection fraction (RVEF) to refer to the amount of blood delivered to the lungs.
During a heartbeat, the heart muscle contracts and relaxes just like any other muscle during activity. The relaxation allows the ventricles, or chambers, to fill with blood. The contraction forces the blood back out. The strength of the heart and clarity of arteries determines how much blood will be pushed out and circulated throughout the body.
The blood in a ventricle right before the contraction is called end-diastolic volume. The volume left in the ventricle after the contraction is the end-systolic volume. If you subtract the end-systolic from the end-diastolic volume, it produces a number called the stroke volume. The ejection fraction is found by dividing the stroke volume by the end-diastolic volume. Effectively, this is the percentage of end-diastolic volume that was forced out with each beat.
For an average, healthy man weighing approximately 154 lbs (70 kg), stroke volume should be approximately 2.4 oz (70 ml) and end-diastolic volume should be around 4.1 oz (120 ml). This makes the ejection fraction 2.4/4.1 or 70/120 which is about 58%. A normal left ventricle ejection fraction (LVEF) ranges from 50 to 70%, but it can be decreased by heart damage or other problems with the heart.
Cardiologists use the ejection fraction to determine a prognosis in patients suffering from a number of ailments, not least among them angina or chest pain. The following numbers are approximate ranges for LVEF and their indications: 50-70% is normal, 36-49% is below normal, 35-40% may indicate systolic heart failure, and below 35% is considered life threatening and irregular. If the ejection fraction is found to be in this lowest category, immediate action is taken to prevent full heart failure.
The ejection fraction is measured by various imaging techniques. An ultrasound, also called an echocardiogram, uses sounds waves to produce images of the heart. Cardiac catheterization involves a thin tube placed into a vein in the leg and into the heart, while magnetic resonance imaging (MRI) uses magnetic fields and radio waves to create cross-sections of the body. Cardiac computed tomography (CT) is a more involved version of an x-ray and a Multiple Gated Acquisition (MUGA) scan uses a small amount of radioactive material in the bloodstream combined with special cameras to create a visualization of the pumping blood.