Heart failure is often diagnosed using an echocardiogram (or echo). An echo is an ultrasound of the heart that shows how well the four chambers are working. One of the important numbers to determine the function of the heart is called an ejection fraction (or EF%). EF is a calculation of the amount of blood pumped from the left ventricle divided by the total amount of blood that is in the heart. Normal EF is 50-70%, reduced is 40-50%, and low is < 40%. The lower the percent, the more severe the heart failure.
The American Heart Association explains more about Ejection Fraction in their short video. Click here to watch the video.