What is cardiac insufficiency?

Vague. This is a vague term which is not typical nomenclature. I assume its referring to a pt with a weak heart called a cardiomyopathy. The pumping function is impaired and thus " insufficient " to meet the bodies needs. Pts like this are prone to episode of cogestive heart failure.
Heart pump. The heart is a pump that supplies blood to the entire body. To perform this function it needs to be able to relax an fill with blood, then contract to pump the blood. Cardiac insufficiency exists when the heart can not perform this function properly.
Heart disease. Cardiac insufficiency is a very old term that is roughly synonomous with congestive heart failure. It hasn't been used for many years and so its use today is archaic.