Congestive heart failure (CHF) is a term used by cardiologists to describe a patient whose heart does not pump enough blood out to the rest of the body to meet the body's demand for energy.

This can be due to either a heart that pumps well but is very insufficient (due to a structural problem), or it can be a result of a weak heart muscle that does not pump a normal amount of blood to the body.

Either situation will lead to backup of blood and fluid into the lungs if the left side of the heart is the problem or backup of blood and fluid into the liver and veins leading into the heart if the right side of the heart is problem.

It is not uncommon for both sides of the heart to fail at the same time and cause backup into both systems simultaneously.

For the purpose of the Cincinnati Children's Hospital Medical Center's Heart Encyclopedia, the focus is on backup or excessive blood flow into the lungs, which is the most common use of the term in pediatrics.