Canine Heart Disease Guide: Managing Mitral Valve Disease and DCM in Dogs

Marty and Laura dive into canine cardiac health, breaking down the causes, symptoms and life-extending treatments for the two most common acquired heart diseases in dogs: mitral valve disease in small breeds and dilated cardiomyopathy (DCM) in large breeds.

• Mitral Valve Disease (Small Breed Dogs):
  • Who it affects: Small breeds like Shih Tzus, Schnauzers and Cavalier King Charles Spaniels.
  • The Cause: Genetic factors lead to “knobby” protrusions on the left-side mitral valve, preventing a proper seal and causing blood to leak backward into the left atrium.
  • Proactive Monitoring: Owners should count their dog’s resting respiratory rate monthly while they are horizontally asleep. Normal is 26 to 32 breaths per minute; rates climbing past 38 to 40 require veterinary attention.
  • Symptoms: Look out for reduced exercise tolerance, weight loss (cardiac cachexia), and a persistent cough (often caused by an enlarged heart pressing on the trachea).
  • Prevention & Care: Excellent dental health and routine brushing can prevent bacteria from latching onto damaged heart valves.
• Dilated Cardiomyopathy / DCM (Large Breed Dogs):
  • Who it affects: Primarily large breeds like Great Danes, Dobermans, Boxers and Newfoundlands, with rare exceptions in small terriers.
  • The Cause: The heart muscle becomes flabby and weak, impairing its ability to contract. DCM can stem from genetic factors, chemotherapy drugs or nutritional deficiencies (taurine and L-carnitine) linked to grain-free or legume-rich diets.
  • Symptoms & Risks: Unlike small dogs, large dogs with DCM are highly prone to dangerous arrhythmias (irregular heartbeats), fainting and sudden acute heart failure.
• Diagnosis and Modern Treatments:
  • Diagnosis is Accessible: Any primary care veterinarian can diagnose an enlarged heart using a standard chest X-ray and a Vertebral Heart Score (VHS) to normalize heart size against the spine.
  • Improved Lifespans: While dogs diagnosed with heart disease historically survived only six months, modern medications can give them two to three more high-quality years.
  • Primary Medications: Treatment frequently relies on Pimobendan (a veterinary-only drug that strengthens heart contractions), ACE inhibitors (enalapril or benazepril), and diuretics like furosemide (Lasix) or spironolactone.
  • Cardiac Emergencies: Tears in the chordae tendineae (fibers holding the valve) can trigger sudden, severe failure. Advanced hospital care can include oxygen, sildenafil (Viagra) for pulmonary hypertension, nitroglycerin, and amlodipine. Note that canine CPR is rarely successful in chronic cardiac arrest, so owners should not harbor guilt if they cannot revive an arresting pet.