Heart murmurs

From Dog

Murmurs, the most common heart disease of dogs, are defined as vibrations caused by disturbed blood flow associated with high flow through normal or abnormal valves of the heart.

In dogs, a murmur can include flow disturbances associated with outflow obstruction or forward flow through stenosed valves or into a dilated vessel. Murmurs can also indicate flow disturbances associated with regurgitant flow through an incompetent valve, septal defect or patent ductus arteriosus[1].

Heart murmurs are graded according to clinical and echocardiographic signs:

  • Grade I: barely audible
  • Grade II: soft but easily auscultated
  • Grade III: intermediate loudness (most haemodynamically important murmurs are at least grade III)
  • Grade IV: loud, with a palpable thrill
  • Grade V: very loud, audible with stethoscope barely touching he chest, with palpable thrill
  • Grade VI: very loud, audible without the stethoscope touching the chest, with palpable thrill

An exclusion of other causes of auscultable murmurs includes other heart sounds (e.g. split sounds, ejection sounds, gallop rhythms, and clicks), abnormal lung sounds and pleural rubs, and anaemia.


  • Physiological: "innocent murmur", usually self-correcting in dogs and often due to anemia, anxiety, fever, etc.
  • Organic:
  1. Systolic -
- left chest wall
- Grade II-IV - cardiomyopathy, aortic stenosis, pulmonic stenosis, Tetralogy of Fallot, atrial septal defects
- Grade V-VI - mitral valve dysplasia, mitral valve endocardiosis, mitral valve bacterial endocarditis
- right chest wall
- Grade II-IV - Aortic stenosis, ventricular septal defect
- Grade III-V - tricuspid valve dysplasia, tricuspid valve endocardiosis, tricuspid valve bacterial endocarditis
  1. Diastolic - bacterial endocarditis (aortic or pulmonic valve), atrial septal defects, ventricular septal defect, mitral or tricuspid valve stenosis (rare)
  2. Continuous - patent ductus arteriosus



  1. Meijer M & Beijerink NJ (2012) Patent ductus arteriosus in the dog: a retrospective study of clinical presentation, diagnostics and comparison of interventional techniques in 102 dogs (2003-2011). Tijdschr Diergeneeskd 137(6):376-383