Why is it called congestive heart failure?

Fluid retention: Because the heart doesn't pump blood well enough when it is "failing", fluid tends to back up in the legs and lungs. This can cause weight gain and difficulty breathing.

Heart Failure: It is called heart failure because the heart fails to pump the blood effectively. Because the blood is not pumped out of the lungs effectively, the fluid backs up in the lungs so the lungs become congested with this excess fluid build up. Thus, the name...

Congested lungs: When the heart isn't able to pump effectively, pressure builds up behind the heart and causes fluid to build up in the lungs causing "congestion".