Equis ISSN 2398-2977

Heart: mitral regurgitation

Synonym(s): Mitral valve regurgitation

Contributor(s): Keith Strickland, Lesley Young


  • Cause:
    • Acquired: degenerative fibrotic thickening, rupture of chordae tendineae, endocarditis, prolapse of valve leaflets, secondary stretching of mitral valve annulus.
    • Congenital: valvular dyslpasia.
  • Signs: systolic murmur, congestive heart failure, cardiac arrhythmias.
  • Diagnosis: auscultation, clinical examination, echocardiography.
  • Treatment: none in most cases; antibiotics for endocarditis; diuretics, vasodilators and positive inotropes for congestive heart failure.
  • Prognosis: good to poor, depending on severity of disease.
Print off the Owner factsheet on Heart murmurs to give to your clients.



  • Most commonly associated wtih dengenerative fibrotic thickening of the valve leaflets   →    mitral valve regurgitation. Etiology is currently unknown.
  • Rarely, acute rupture of a supporting chordae tendineae   Chordae tendineae: rupture  : rupture of a major chorda in severe acute valve insufficiency, rapid increases on left atrial pressure, pulmonary venous hypertension and left-sided heart failure.
  • Prolapse of a mitral valve leaflet into the left atrium results in mitral valve regurgitation, the precise etiology of the condition is unknown, but it is generally benign and non-progressive.
  • Secondary mitral valve regurgitation results from stretch of the mitral valve annulus, in any condition that results in left ventricular dilation, eg cardiomyopathy   Heart: cardiomyopathy  , myocarditis   Heart: myocarditis  , chronic left-to-right shunts and aortic regurgitation   Heart: aortic regurgitation      Heart: aortic regurgitation 01 - color echocardiograph  .
  • Mitral regurgitation +/- chordae tendineae rupture can result from bacterial endocarditis   Heart: endocarditis  , but this is rare.

Predisposing factors


  • Bacterial endocarditis   Heart: endocarditis  .
  • Eccentric cardiac hypertrophy of athletic training can mildly increase severity of valve regurgitation.
  • Dilation of the left ventricle and mitral annulus due to volume overload or myocardial failure.


  • Severe mitral regurgitation   →   left atrial volume and, ultimately, pressure overload.
  • Left ventricular systolic dysfunction   →    reduced cardiac output and poor perfusion.
  • Left atrial stretch promotes the development of premature atrial contractions.
  • Increased left atrial mass, stretch and myocardial remodeling promote the development of atrial fibrillation   Heart: atrial fibrillation  .
  • Left atrial pressure increases   →    pulmonary hypertension and then   →    progressive pulmonary edema   Nose: pulmonary edema - left heart failure    Thorax: cardiogenic pulmonary edema - radiograph   and possibly pulmonary arterial hypertension, right ventricular pressure overload and right-sided congestive heart failure.
  • Right ventricular pressure overload   →    tricuspid valve insufficiency.
  • Right ventricular pressure overload   →    secondary right sided congestive failure and systemic venous hypertension (ventral edema and jugular engorgement   Abdomen: ventral edema 01    Abdomen: ventral edema 02  ).


  • Variable.
  • In some/most horses, mild mitral regurgitation never significantly progresses.
  • If decompensation occurs and there are signs of congestive heart failure, progression is usually very rapid.
  • Even in severe progressive mitral valve regurgitation, progression to decompensation can take years.



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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Duz M, Philbey A W & Hughes K J (2013) Mitral valve and tricuspid valve dysplasia in a 9-week-old Standardbred colt. Equine Vet Educ 25 (7), 339-344 VetMedResource.
  • Patteson M (2010) Prepurchase examination in horses: detection and significance of heart murmurs. In Pract 32 (9), 438-443 VetMedResource.
  • Stevens K B et al (2009) Effect of left-sided valvular regurgitation on mortality and causes of death among a population of middle-aged and older horses. Vet Rec 164 (1), 6-10 PubMed.
  • Buhl R, Ersboll A K, Eriksen L & Koch J (2005) Use of color Doppler echocardiography to assess the development of valvular regurgitation in Standardbred trotters. JAVMA 227 (10), 1630-1635 PubMed.
  • Kriz N G, Hodgson D R & Rose R J (2000) Prevalence and clinical importance of heart murmurs in racehorses. JAVMA 216 (9), 1441-1445 PubMed.
  • Young L E & Wood J L N (2000) The effects of age and training on murmurs of atrioventricular valvular regurgitation in young Thoroughbreds. Equine Vet J 32 (3), 195-199 PubMed.
  • Reef V B, Bain F T & Spencer P A (1998) Severe mitral regurgitation in horses: clinical, echocardiographic and pathological findings. Equine Vet J 30, 18-27 PubMed.
  • Reef V B (1995) Heart murmurs in horses: determining their significance with echocardiography. Equine Vet J Suppl 19, 71-80 PubMed.
  • Patteson M W & Cripps P J (1993) A survey of cardiac auscultatory findings in horses. Equine Vet J 25, 409-417 PubMed.
  • Else R W & Holmes J R (1972) Cardiac pathology in the horse. 1. Gross pathology. Equine Vet J (1), 1-8 PubMed.
  • Else R W & Holmes J R (1972) Cardiac pathology in the horse. 2. Microscopic pathology. Equine Vet J (2), 57-62 PubMed