An echocardiogram is an ultrasound of the heart, much like what expectant mnothers get of their uterus. This should *not* be confused with an ECG which looks at the electrical conduction of the heart. The ultrasoundcan show the flow of blood between the chambers of the heart, so that any abnormalities such as backflow, or holes in the heart can be detected. If you see an echocardiogram performed, different colours show up which indicate the speed and direction of the movement of blood. The ejection fracrtion can be estimated from and echocardiogram, and normal EF is more than 55%. This refers to how much of the blood is pushed out of the chamber of the heart when it beats, to go around the body. The two main chambers of the heart are called ventricles, the right ventricle pumps 'used' blood to the lungs to remove carbon dioxide and take on oxygen. The 'fresh' blood comes back to he heart and eventually leaves via the left fentricle, to go all around the body. Hence why LV function is usually referred to, if the ejection fraction is not stated on which side. The two are normally about equal, but there will be slight discrepancies beat to beat in even the most health individual. So to measure it, you simply measure how much blood is in the cham,ber before it beats and after it beats, and use these two figures to make a fraction, the ejection fraction. Obviously you can use these numbers to make a percentage as well, since someone with a small heart would have lower numbers, but perhaps a very large percentage and so would be healthy. So it is referred to as a fraction but is given as a percentage. So a low EF (less than 55%) means that less blood is being pumped out of the heart each time it beats compared to normal. A lower EF often indicates that the heart muscle has lost some of its ability to contract, usually from heart disease, such as after a heart attack. Should the EF fall too low, it is said that the patient is in heart failure (usually noted as CCF or congestive cardiac failure), meaning that the heart is not able to cope with the amount of blood entering it and can't push enough back out.