Mitral Valve (Left Atrioventricular Valve)
A dual-leaflet one-way heart valve that prevents blood from flowing backward from the left ventricle into the left atrium during heart contractions.
💬 In Plain English
The mitral valve is a delicate, paper-thin, parachute-like valve separating the top and bottom chambers on the left side of the heart (the left atrium and left ventricle). It consists of two smooth leaflets tethered to tiny heart muscle anchors by fibrous strings called chordae tendineae (the "heartstrings"). When the left ventricle contracts to pump freshly oxygenated blood out to the body, the mitral valve snaps tightly shut to prevent blood from leaking backward. In older small dogs, the valve leaflets slowly thicken and warp, causing a leaky valve (MMVD) and heart murmur.
🔬 Clinical & Technical Depth
For Vets & TechniciansFormal Clinical Definition
Bicuspid atrioventricular valve complex comprising an anterior (parietal) leaflet, a posterior (septal) leaflet, chordae tendineae, and papillary muscles. Ensures unidirectional forward flow of oxygenated pulmonary venous blood into systemic circulation.
Why Veterinarians Use It
Veterinarians listen to the mitral valve by placing their stethoscope over the left fifth intercostal space at the heart apex, listening for systolic regurgitation murmurs.
Clinical Context Encountered
Discussed whenever a veterinarian discovers a new heart murmur in an older small-breed dog or investigates coughing and exercise fatigue.
Clinical Reference Guide (Anatomical Structure)
Anatomical Location
Left side of the heart, forming the junction between the left atrium (inflow) and left ventricle (pumping chamber).
Normal Physiological Function
Opens widely during ventricular diastole to allow oxygenated blood from lungs to fill the left ventricle; seals completely during ventricular systole to prevent retrograde regurgitation into the left atrium.
🐕 vs 🐈 Species Differences
Small dog breeds (Cavaliers, Poodles, Chihuahuas) have an overwhelming genetic susceptibility to degenerative myxomatous mitral valve disease (MMVD), whereas cats more frequently suffer from myocardial diseases (HCM) rather than primary valve degeneration.
- •Acute rupture of a chordae tendineae string can cause sudden massive valve failure, sending a stable dog into fulminant, life-threatening pulmonary edema within hours.
❓ Questions to Ask Your Veterinarian
Take these actionable questions with you to your next clinic visit or appointment:
- 1What grade (1 to 6) is the heart murmur heard over the mitral valve?
- 2Does an echocardiogram show thickening of the valve leaflets or prolapse back into the atrium?
- 3Are the chordae tendineae intact, or is there any sign of a ruptured chord?
- 4Are the left atrium and left ventricle enlarged from backward volume overload?
Academic & Clinical References
- Cardiac Anatomy and Valve Function in AnimalsOrganization: Merck Veterinary Manual • Accessed: 2026-01-10https://www.merckvetmanual.com