NAVLECardiovascular·⏱ 12 min read·📅 Mar 28, 2026·by NAVLE Exam Prep Team·👁 2
Canine Congestive Heart Failure (CHF): Complete NAVLE Study Guide
Canine CHF shows up on the NAVLE constantly, and it almost always comes down to three things: knowing your breeds, knowing your staging, and knowing your drugs. Get those right and you'll handle whatever question they throw at you.
The Two Main Causes
MMVD
Myxomatous Mitral Valve Disease
Breeds: CKCS, Poodles, Dachshunds, small breeds
Mechanism: Valve thickening → MR → LA enlargement
FS: Usually preserved (>25%)
~75% of canine cardiac disease
DCM
Dilated Cardiomyopathy
Breeds: Doberman, Great Dane, Boxer, Irish Wolfhound
NAVLE Pearl
The signalment alone points you to the answer. Small breed + mitral murmur + LA enlargement on rads = MMVD. Large breed + weak dilated heart + arrhythmias = DCM. Read the signalment before the question body.
ACVIM Staging — Know This Cold
The 2019 ACVIM Consensus Guidelines divided MMVD into four stages. The boards test whether you know when to start treatment — not just which drugs to use.
Stage
Definition
Treatment
A
At-risk breed, no murmur yet
None — monitor
B1
Murmur present, no cardiac remodeling
None — monitor q12 months
B2
Murmur + remodeling: LA:Ao ≥1.6 and VHS ≥10.5
Start pimobendan (EPIC trial)
C
Current or past CHF signs
Furosemide + pimobendan + ACE inhibitor
D
Refractory CHF
Add spironolactone, CRI furosemide, O²
The EPIC trial (2016) changed everything for Stage B2. Before EPIC, you waited until CHF to start pimobendan. Now you start it in asymptomatic dogs with significant remodeling — it delays onset of CHF by about 15 months. That finding is highly testable.
Clinical Signs: Left vs Right-Sided
Left-Sided Failure
• Soft, moist cough (worse at night)
• Exercise intolerance
• Tachypnea, orthopnea
• Pulmonary crackles
Rads: perihilar pulmonary edema
Right-Sided Failure
• Ascites
• Pleural effusion (less common in dogs)
• Jugular venous distension
• Hepatomegaly, peripheral edema
Rads: hepatomegaly + ascites
NAVLE Tip
Cough + exercise intolerance + rads showing LA enlargement and perihilar edema = left-sided. Ascites on the same dog = right-sided or biventricular. Know which direction the fluid goes.
Diagnostics
Thoracic radiographs — first step in respiratory distress. Look for cardiomegaly (VHS >10.5), left atrial enlargement on lateral view (the caudal cardiac waist disappears), and perihilar alveolar pattern for pulmonary edema.
Echocardiography — gold standard for staging. Gives you LA:Ao ratio, fractional shortening (FS), and confirms structural disease. FS <25% = systolic dysfunction in dogs.
NT-proBNP — rises with myocardial wall stretch. Useful to differentiate cardiac from respiratory dyspnea before echo is available. The QUEST trial validated its use in MMVD.
Empty stomach — bioavailability drops 30% with food
Enalapril
ACE inhibitor
0.5 mg/kg PO BID
Monitor renal values + K+
Spironolactone
Aldosterone antagonist
2 mg/kg PO SID
Anti-fibrotic; Stage C/D
Digoxin
Cardiac glycoside
Target level 0.8–1.2 ng/mL
Rate control in AFib; narrow TI
Classic NAVLE Trap
Dog in acute pulmonary edema → furosemide IV is correct. Next question: what do you add for long-term management? Answer: pimobendan — not digoxin, not ACE inhibitor alone. Pimobendan is now the cornerstone of canine CHF management.
Prognosis
Stage B2 dogs started on pimobendan: median time to CHF onset ~3 years. Stage C with optimal therapy: median survival 9–12 months. Stage D: weeks to a few months.
Atrial fibrillation in a Doberman with DCM = emergency. Rate control with diltiazem or digoxin + aggressive diuresis. AFib significantly shortens survival in large breed DCM.
Quick Reference
MMVD = small breeds (CKCSs); DCM = large breeds (Dobermans)
Test yourself before moving on. Click an answer to reveal the explanation.
Question 1
A 9-year-old Cavalier King Charles Spaniel has a loud left apical systolic murmur. Thoracic radiographs show a vertebral heart sum of 11.2 and LA:Ao ratio of 1.7. The dog is asymptomatic with no history of coughing or exercise intolerance. What is the most appropriate management?
Explanation
This dog is ACVIM Stage B2 — murmur present with significant cardiac remodeling (VHS 11.2 >= 10.5 and LA:Ao 1.7 >= 1.6) but no clinical CHF signs. The EPIC trial (2016) showed pimobendan alone at Stage B2 delays onset of clinical CHF by approximately 15 months. Furosemide and ACE inhibitors are added at Stage C when CHF signs appear. Surgery is not a standard treatment for MMVD.
Question 2
A 7-year-old Doberman Pinscher presents with acute weakness and respiratory distress. Auscultation reveals a soft systolic murmur and gallop rhythm. Echo shows fractional shortening of 18% and diffuse myocardial hypokinesis. Which condition is most likely?
Explanation
DCM is the classic diagnosis in a Doberman with a weak, dilated heart. FS < 25% confirms systolic dysfunction. MMVD typically shows preserved systolic function. HCM causes concentric thickening, not dilation, and is rare in dogs. Pericardial effusion causes muffled heart sounds and does not produce a systolic murmur. Aortic stenosis causes a left basilar ejection murmur with preserved LV function.
Question 3
A dog with Stage C CHF (MMVD) is discharged on furosemide and pimobendan. Which instruction about pimobendan administration is most important to give the owner?
Explanation
Pimobendan bioavailability drops approximately 30% when given with food. It must be given on an empty stomach, ideally 1 hour before a meal, at BID intervals. Once daily dosing is insufficient. Refrigeration is not required for standard tablet formulations. Crushing into food directly contradicts the empty-stomach requirement and reduces efficacy.
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