Heart disease (dogs)
Most often degenerative valve disease in small breeds or dilated cardiomyopathy in large breeds. Progressive, manageable, eventually causes congestive heart failure.
In dogs, the two most common heart diseases are very different. **Mitral valve disease** (myxomatous mitral valve disease, MMVD) affects small-breed dogs — Cavalier King Charles Spaniels are the poster breed, with up to 50% affected by age 5 and most by age 10. **Dilated cardiomyopathy** (DCM) affects large breeds — Dobermans, Boxers, Great Danes, Newfoundlands.
Both progress quietly for years before signs appear. Routine cardiac auscultation at annual exams catches murmurs early. Once a murmur is detected, periodic echocardiography assesses progression.
Early-stage treatment is increasingly pre-symptomatic — the EPIC trial in Cavaliers showed that starting pimobendan before clinical signs extends time-to-heart-failure by years. Talk to your vet about evidence-based early intervention if your dog has a murmur.
Late stage (congestive heart failure): coughing especially at night or after lying down, exercise intolerance, fast breathing at rest (more than 30 breaths per minute), abdominal swelling. This stage needs diuretics, ACE inhibitors, pimobendan, sometimes other medications, and careful monitoring.
Counting your dog's resting respiratory rate weekly is one of the most useful home monitoring habits in heart disease — early rise in rate predicts decompensation days before crisis.