Disease of the heart is basically either something the pet is born with or is acquired with age. Cats basically have only one common heart problem called cardiomyopathy. This is a heart muscle problem where the muscle is weak and thin and the pressure inside the heart makes it dilate. These kitties hearts beat weaker and less efficiently than their normal-hearted kitty pals. Lack of taurine in the kitty diet may be a culprit in causing feline cardiomyopathy.
Dogs often have problems with their heart valves.
The most common valve problem that dogs have is mitral valve insufficiency. This valve separates the left atrium from the left ventricle. The atrium is the lower-pressure top chamber and the ventricle is the heavily muscled bottom chamber. As I listen to the left chest wall, I hear the heart making a whooshing sound. This is a common finding on the physical exams I give older pets.