NAVLE Cardiology High-Yield Guide: Heart Disease Questions Across Species

Cardiology questions on the NAVLE are designed to test your ability to synthesize signalment, auscultation findings, diagnostic results, and pharmacology all at once. A question rarely asks "what is DCM?" — it asks: a six-year-old Doberman presents with a grade III/VI left apical systolic murmur and a gallop. Thoracic radiographs show cardiomegaly. What is the most appropriate next step? To answer that confidently, you need the breed-disease link, the murmur character, the diagnostic approach, and the drug arsenal all in one mental map.

This guide organizes NAVLE cardiology high-yield content into the exact framework the exam uses: species and breed predispositions, auscultation findings, staging systems, and first-line treatments. Work through each section, memorize the key tables, and you will be equipped to handle every veterinary cardiology NAVLE question that appears.

Cardiac Auscultation Basics: What the Exam Expects You to Know

Before diving into individual diseases, make sure the auscultation fundamentals are solid. The NAVLE will describe a murmur and expect you to localize it, characterize it, and generate a differential list.

Murmur Grading (I–VI)

• Grade I: barely audible, heard only in a quiet room, focal
• Grade II: soft but consistently audible
• Grade III: moderate intensity, no thrill
• Grade IV: loud, no thrill or thrill present
• Grade V: very loud, palpable thrill
• Grade VI: audible with stethoscope held off chest wall, palpable thrill

A thrill is a palpable vibration and implies at least a Grade IV murmur. On NAVLE questions, if a thrill is described, the murmur is significant and warrants workup.

Point of Maximum Intensity (PMI)

The PMI tells you which valve and which side of the heart is involved. The key landmarks:

• Left apex (mitral area): 5th intercostal space — mitral valve, left AV valve disease
• Left base (aortic area): 4th ICS, dorsal — aortic outflow, SAS, PDA
• Left base (pulmonic area): 2nd–3rd ICS — pulmonic stenosis
• Right cranial (tricuspid area): 3rd–4th ICS — VSD, tricuspid regurgitation

Split Sounds and Gallop Rhythms

A gallop rhythm (S3 or S4) in a dog or cat indicates myocardial disease and poor compliance. In cats, a gallop may be the only auscultatory abnormality in HCM — no murmur required. A split S2 can indicate pulmonary hypertension. A continuous (machinery) murmur heard best at the left base indicates patent ductus arteriosus.

Canine Myxomatous Mitral Valve Disease (MMVD)

Myxomatous mitral valve disease (MMVD, formerly called endocardiosis or chronic valvular disease) is the most common acquired cardiac disease in dogs. It accounts for the majority of canine cardiac cases on the NAVLE.

Signalment and Pathophysiology

Primarily affects small breeds — Cavalier King Charles Spaniel (CKCS, earliest onset), Dachshund, Miniature Poodle, Chihuahua, Maltese. The mitral valve leaflets develop myxomatous degeneration, thicken, and prolapse, causing mitral regurgitation. Volume overload leads to left atrial and ventricular enlargement, eventually precipitating left-sided CHF.

Murmur: left apical systolic murmur, grade I–VI. The severity of the murmur correlates roughly (not perfectly) with regurgitation severity.

ACVIM Staging — Know Every Stage

The 2019 ACVIM Consensus Guidelines define four stages. The NAVLE tests these directly:

• Stage A: high-risk breed, no murmur yet — no treatment, monitor
• Stage B1: murmur present, no radiographic or echocardiographic cardiomegaly — no medication, recheck every 12 months
• Stage B2: murmur present + radiographic/echo evidence of cardiomegaly (enlarged LA) — start pimobendan
• Stage C: current or past signs of CHF — furosemide (acute: IV; chronic: oral), pimobendan, ACE inhibitor, spironolactone
• Stage D: refractory CHF despite standard therapy — escalate diuretics, consider add-on agents

The EPIC trial established that pimobendan started at Stage B2 delays onset of CHF by approximately 15 months. This is the highest-yield fact for MMVD on the exam.

Key Drugs: MMVD

• Pimobendan: inodilator — positive inotrope (PDE-III inhibitor) + vasodilator (calcium sensitizer); improves stroke volume and reduces afterload; give on empty stomach
• Furosemide: loop diuretic; first-line for pulmonary edema in acute CHF; monitor potassium and renal function
• ACE inhibitor (enalapril, benazepril): reduces afterload and aldosterone; added at Stage C
• Spironolactone: aldosterone antagonist; added at Stage C or D; mild diuretic, potassium-sparing

Canine Dilated Cardiomyopathy (DCM)

Dilated cardiomyopathy is the second most common acquired cardiac disease in dogs and the primary myocardial disease of large and giant breeds. It is characterized by systolic dysfunction — the ventricles dilate and contractility is severely reduced.

Breed Predispositions

• Doberman Pinscher: most common large breed affected; occult phase — may have DCM with ventricular arrhythmias for months to years before showing signs
• Boxer: arrhythmogenic right ventricular cardiomyopathy (ARVC / Boxer cardiomyopathy) — ventricular tachycardia, syncope, sudden death; structural changes secondary
• Great Dane, Irish Wolfhound, Scottish Deerhound: classic DCM with rapid progression
• Atypical breeds (Golden Retriever, Labrador, others): grain-free diet link — taurine deficiency or DCM-like syndrome; NAVLE may test the grain-free/taurine/DCM association

Auscultation

The murmur of DCM is often soft (grade I–III) or absent because the ventricle is too dilated and weak to generate high-velocity regurgitant flow. The key auscultatory finding is a gallop rhythm (S3), particularly in Dobermans. Atrial fibrillation is common in advanced disease.

Occult DCM in Dobermans

Dogs can have echocardiographic DCM and ventricular premature contractions (VPCs) without clinical signs for 1–4 years. Screening with annual Holter monitor (24-hour ECG) and echocardiogram is recommended for Dobermans over 2 years. The Doberman DCM study (PROTECT trial) showed pimobendan delays onset of CHF from the occult phase.

Treatment: DCM

• Pimobendan: start in occult phase once criteria met
• Furosemide: for CHF signs
• ACE inhibitor
• Mexiletine: class Ib antiarrhythmic; used for Doberman VPCs and ventricular tachycardia
• Sotalol: used in Boxers with ARVC for VT management
• Taurine supplementation: for grain-free diet associated DCM in atypical breeds

Feline Hypertrophic Cardiomyopathy (HCM)

HCM is the most common cardiac disease in cats and the disease most likely to test your knowledge of feline-specific cardiology on the NAVLE. The pathology, clinical presentation, and drug choices all differ significantly from canine cardiology.

Signalment and Genetics

• Maine Coon: autosomal dominant MYBPC3 mutation; genetic test available
• Ragdoll: different MYBPC3 mutation; genetic test available
• Any cat can develop HCM; middle-aged to older males most commonly affected in the general population

Pathophysiology and Dynamic Obstruction

The left ventricular wall becomes hypertrophied, reducing diastolic filling (diastolic dysfunction). The hypertrophied septum can cause systolic anterior motion (SAM) of the mitral valve, creating a dynamic left ventricular outflow tract obstruction and a functional murmur. SAM worsens with tachycardia, excitement, and catecholamine release — relevant to anesthesia risk.

Auscultation in Cats

Cats with HCM may have:

• A systolic murmur (often left sternal border or apex)
• A gallop rhythm (S4 most common in cats) — this may be the only finding
• No murmur — silent HCM is common and clinically significant

Aortic Thromboembolism (ATE)

Cats with HCM and left atrial enlargement are at high risk for thrombus formation and ATE — a devastating complication. The classic presentation is acute hind limb paresis/paralysis with the "5 P's":

1. Pain — vocalization, distress
2. Pulseless — absent femoral pulse
3. Paralysis — rear limb paresis or plegia
4. Pallor — pale, cyanotic nail beds and foot pads
5. Poikilothermia — cold extremities

Treatment is supportive; prognosis is guarded. The FATCAT trial showed clopidogrel is superior to aspirin for prevention of recurrent ATE in cats. Know this trial name and drug for the exam.

Drug Choices in Feline HCM

• Atenolol: beta-1 selective blocker; reduces heart rate, decreases SAM, improves diastolic filling time
• Diltiazem: calcium channel blocker; rate control, improves diastolic relaxation
• Clopidogrel: antiplatelet; ATE prevention (FATCAT trial)
• Furosemide: for CHF / pleural effusion
• ACE inhibitors: NOT indicated in cats without CHF; can worsen renal function — a common NAVLE trap
• Pimobendan: generally avoided in obstructive HCM (SAM); can worsen outflow obstruction

Canine Arrhythmias: High-Yield ECG Findings

Atrial Fibrillation

Atrial fibrillation (AF) is the most clinically significant arrhythmia in large-breed dogs. It produces an irregularly irregular rhythm with no discernible P waves and variable R-R intervals. Large breeds predisposed include Great Dane, Irish Wolfhound, Newfoundland, and Saint Bernard. AF in these breeds is usually secondary to DCM or severe cardiomegaly.

Treatment goal is rate control, not cardioversion (because underlying disease is present). Options include digoxin alone or in combination with diltiazem. If AF is paroxysmal in a structurally normal heart (lone AF), cardioversion with sotalol may be attempted.

Sick Sinus Syndrome

Sick sinus syndrome features alternating bradycardia and tachycardia ("bradycardia-tachycardia syndrome"). Classically seen in Miniature Schnauzers and Cocker Spaniels. Clinical signs include syncope, weakness, and exercise intolerance. Medical management is unreliable; definitive treatment is pacemaker implantation.

Third-Degree (Complete) AV Block

Complete AV block means no impulses conduct from atria to ventricles. On ECG: P waves and QRS complexes are completely dissociated — regular P-P intervals, regular R-R intervals, but no relationship between them. The ventricles are driven by a slow escape rhythm (20–40 bpm in dogs). Affected animals are often profoundly bradycardic, weak, or syncopal. Treatment: permanent pacemaker. Atropine and sympathomimetics are only temporizing measures.

Ventricular Premature Contractions (VPCs)

VPCs appear as wide, bizarre QRS complexes without a preceding P wave, occurring earlier than expected. Runs of VPCs are ventricular tachycardia. Clinically significant in Dobermans (DCM screen) and Boxers (ARVC). Treat with mexiletine in Dobermans or sotalol in Boxers when sustained VT or high VPC burden on Holter is confirmed.

Murmur Location, Timing, and Disease: Quick Reference Table

Equine Cardiology: NAVLE High-Yield Points

Atrial Fibrillation in Horses

AF is the most common performance-limiting arrhythmia in horses. This fact is directly tested on the NAVLE. Affected horses may be asymptomatic at rest but show poor performance, exercise intolerance, or respiratory distress under work. The rhythm is irregularly irregular; the clinical finding is variable cardiac rhythm on auscultation.

Cardioversion is indicated if:

• AF has been present for less than 4 months (less fibrosis, better success rate)
• No underlying structural cardiac disease
• Potassium is within normal range before treatment

Methods: quinidine sulfate (oral via nasogastric tube — traditional method) or flecainide IV (newer, faster). Quinidine can cause GI signs, laminitis, and paradoxical tachycardia — monitor closely. If cardiac disease is present (e.g., mitral or tricuspid regurgitation), do NOT attempt cardioversion.

Equine Murmurs and Venous Hum

Incidental murmurs are extremely common in horses. A physiologic (functional) murmur is a soft systolic murmur heard at rest or associated with high cardiac output, with no pathological significance. A venous hum is a low-pitched continuous sound heard at the jugular vein, not over the heart — it is a normal finding in horses and cattle. Do not confuse it with a cardiac murmur.

Significant murmurs include aortic regurgitation (early diastolic, left base, associated with poor performance in racehorses) and mitral regurgitation. Echocardiography is required to characterize the lesion and guide prognosis for performance horses.

Bovine and Large Animal Cardiology

Traumatic Reticulopericarditis (Hardware Disease)

Traumatic reticulopericarditis (TRP) is caused by ingested metal hardware penetrating the reticulum wall and migrating to the pericardial sac. It is a classic NAVLE large animal cardiology topic.

Clinical signs of pericarditis:

• Muffled heart sounds bilaterally
• Jugular venous distension and ventral edema (brisket edema)
• Pericardial friction rub (early) or "washing machine" sounds (fluid accumulation)
• Tachycardia, fever, decreased milk production, anorexia
• Pain on deep palpation of xiphoid or going downhill

Diagnosis: rumenography / metal detector (positive magnet test for reticulum hardware), ultrasonography showing pericardial effusion, elevated fibrinogen and WBC. Pericardiography shows fibrin strands.

Treatment: systemic antibiotics (penicillin), placement of a rumen magnet (prophylactic and therapeutic for reticular hardware), pericardiostomy and lavage. If the cow has chronic fibrinous pericarditis, pericardiectomy may be required but prognosis is guarded for production animals. Salvage slaughter is often chosen.

Bovine Endocarditis

Bacterial endocarditis in cattle most commonly affects the right-sided valves (tricuspid). Organisms include Trueperella pyogenes and Streptococcus spp. Clinical signs: right-sided CHF signs (ventral edema, jugular pulsation), fever, murmur. Prognosis is poor; long-term penicillin therapy may result in temporary improvement but recurrence is common.

Vagal Indigestion vs. Cardiac Disease

A common NAVLE question involves differentiating vagal indigestion (functional ileus from reticular adhesions) from hardware disease. Both can result from hardware penetration. Key distinction: vagal indigestion presents with rumen distension ("papple shape" in some classifications) and altered forestomach motility, while hardware disease presents with the pericarditis signs above. Both may show decreased rumen motility and anorexia.

Congenital Heart Defects: Species, Signs, and Treatment

The Eisenmenger's syndrome concept is high-yield: a left-to-right shunt that has been present long enough to cause pulmonary hypertension will reverse to a right-to-left shunt, producing cyanosis. At this point, surgical closure is contraindicated because the pulmonary hypertension, not the defect, is the limiting factor.

CHF Management and Emergency Treatment

Acute decompensated CHF is a true emergency. The NAVLE may present a dog in acute respiratory distress with pulmonary edema and ask for the immediate treatment plan. Know this protocol cold:

1. Oxygen supplementation — flow-by or oxygen cage immediately; minimize stress; do not perform diagnostics until stabilized
2. Furosemide IV or IM — furosemide is the cornerstone of acute CHF treatment; IV bolus (2–4 mg/kg dog, 1–2 mg/kg cat) or CRI; reassess respiratory rate within 1 hour
3. Nitroprusside or nitroglycerin — vasodilators to reduce preload and afterload in severe acute CHF; nitroprusside CRI for refractory cases; nitroglycerin ointment for field/transport
4. Pimobendan — continue or start if not already on board; improves cardiac output immediately
5. Thoracocentesis or abdominocentesis — perform once stable if pleural or abdominal effusion is identified; cats commonly develop bilateral pleural effusion rather than pulmonary edema in left-sided CHF
6. Transition to oral maintenance — once respiratory rate normalizes, transition to oral furosemide + pimobendan + ACE inhibitor (Stage C protocol)

Cardiac Drugs Quick Reference