Congestive Heart Failure (CHF) is a clinical condition which is the final result of severe heart disease. It is usual that when a dog has heart failure, heart disease is also present in the body. However, it is true that in some cases, heart disease can be present, but never lead to congestive heart disease.
When high diastolic pressures in the heart build up into the veins and capillaries, then congestive heart failure can occur, which in turn causes a leakage of fluid out of those vessels.