Congestive heart failure is a problem which affects all types of dogs, but may be caused by different problems in some breeds. Smaller dogs are most likely to develop congestive heart failure from valve problems, while large breeds often suffer from canine dilated myopathy, a condition where the heart becomes less efficient. Congestive heart failure may appear to occur suddenly, but actually happens in several identifiable stages.
Dogs in early stages of congestive heart failure may tire easily and have an overall decrease in activity level. They may appear to be lethargic. The reduction in heart function makes it hard for them to stay active. People often ignore these signs, since they look much like the normal "slowing down" process which occurs as a dog ages. Younger dogs with signs of lethargy are more likely to receive treatment.
The ability of the heart to circulate oxygen through the blood often affects the lungs. As the heart works harder to function and the left ventricle begins to fail, blood and fluid may back up in the lungs, filling the small spaces normally reserved for air. An enlarging heart may also put pressure on the windpipe, causing coughing and difficulty breathing. This type of cough is often worst at night and when the dog is resting. Dogs may also cough up red fluid, a condition called pulmonary oedema.
As the right ventricle fails and congestive heart failure progresses, fluid may leak into the abdomen. Dogs in this stage of congestive heart failure may develop a swollen abdomen, causing a potbellied look. Fluid may also accumulate in the legs, causing swelling there and in the chest cavity. This swelling can camouflage other symptoms of congestive heart failure, including weight and muscle loss. Coughing may be much more severe in this stage.
Dogs in the late stages of congestive heart failure may display colour changes in the gums and tongue. When resting, these animals have red mouths with prominent veins. When they exert themselves, the tongue and gums may turn purplish. Some dogs faint with exertion. Dogs in this stage often have loud heart murmurs, loud breathing, a weak pulse and an elevated heart rate. They often have prominent ribs and spines.