The purpose of the heart is to provide oxygen and nutrients to the rest of the body. Congestive Heart Failure (or CHF) is the failure of the heart to do this adequately. CHF occurs when cardiac output, or the flow of blood from the heart, decreases. Congestive Heart Failure is also when fluid backs-up behind the failing ventricle or fluid back up together with decreased cardiac output.
Time-dependent heart failure is either sudden or develops gradually.
Acute heart failure occurs suddenly. Acute heart failure happens if a large enough part of the heart muscle dies, which means the heart cannot pump out enough blood, resulting in heart failure and pulmonary edema. Breathing becomes very difficult and can lead to death. When a heart valve suddenly stops functioning, this is also acute heart failure, as when the chordae tendineae, which are the muscle and cord that help the mitral valve function properly, rupture all of a sudden.
It's called Chronic heart failure when the heart failure that develops gradually. The symptoms begin subtly but become more acute over time.