The heart has four chambers through which blood pumps. Newly oxygenated blood is pumped from the lungs to the left atrium and left ventricle and out through the aorta to circulate through the rest of the body. After the oxygen has been used, the blood returns through the veins to the right atrium and right ventricle into the lungs to be re-oxygenated.

    Systolic heart failure (left-sided heart failure): When the heart loses strength on the left side (left ventricle) and cannot pump the blood into circulation, it is called systolic heart failure or left-sided heart failure. When this occurs, the heart becomes dilated and weak. The strength of the heart muscle can be measured with an echocardiogram that measures the ejection fraction. An ejection fraction of greater than 55% is normal. The term congestive heart failure, or CHF, refers to the accumulation of fluid in the tissues. Fluid can accumulate in the legs causing swelling (edema), into the lungs causing pulmonary edema, or into the abdomen where it is called ascites. A type of heart failure termed acute decompensated heart failure is an emergency.

    Diastolic heart failure (right-sided heart failure): The second type of heart failure is diastolic heart failure, characterized by the heart becoming thicker and stiffer. When this happens, the left ventricle cannot fill with sufficient blood, and not enough blood is pumped into circulation, even if the pumping action is still strong. This is why diastolic heart failure is sometimes referred to as heart failure with preserved ejection fraction (PEF), or right-sided heart failure. If the signs and symptoms of heart failure are present and the ejection fractions is greater than 50%, diastolic heart failure may be considered, especially if an echocardiogram shows the heart muscle is thickening.