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I’ve detected a murmur – What should be my next step?


One of the most common inquiries I receive pertains to when an animal with a murmur should be referred. Consequently, I’ve compiled a concise blog post on the subject.

Let’s start by understanding what a murmur actually signifies. Under normal circumstances, blood flow through the heart is smooth (laminar). However, any disruption to this flow causes it to become turbulent (non-laminar), resulting in vibrations that manifest as sounds—these are the murmurs we detect on the surface of our patients. Therefore, it’s crucial to identify what could cause such disruptions in order to assess their significance. Essentially, anything that forces blood to flow through a narrower space than usual, such as narrowings, leaks, abnormal holes, or accelerated blood flow, can lead to murmurs.

With this basic understanding of murmurs established, the next step is determining whether they are pathological or non-pathological. What information do we need to make this determination? There are four key considerations:

1. Signalment:

Flow murmurs (generally non-pathological) are typically found in younger dogs. They tend to be soft, usually grade 1 or 2, and disappear when the animals reach 6 months of age. As long as the animals are healthy and free of any clinical symptoms, they can just be observed until they disappear with age. Certain breeds of dogs and cats are predisposed to specific cardiac conditions, the first sign of which may be a murmur. Knowing the breed can help gauge the relevance of the murmur. Therefore, familiarizing yourself with congenital defects associated with various breeds is advisable.

2. Clinical signs:

While some significant murmurs may initially present without obvious symptoms, it’s important to be aware of signs that may accompany pathological murmurs. These may include exercise intolerance, rapid breathing due to pulmonary odema, arrhythmias, weakness or collapse, poor pulse quality, and cyanosis. Any murmur accompanied by these symptoms warrants assessment.

3. Murmur intensity & location:

Murmurs are graded from 1 to 6, with 6 being the loudest. If you can feel a thrill it will be a 5 or 6 and should always be investigated. Murmurs of grade 3 or higher, especially if new, merit further evaluation. Mitral valve disease will not be classed as Stage B2 until the associated murmur is 3 or above. With older, small dogs it is therefore worth further assessment so that a decision can be made under the EPIC study on whether they merit starting medication.

Additionally, assessing the murmur’s location—whether left or right, and apical or base—is crucial. For instance, apical murmurs in older, small dogs often indicate mitral valve disease, while basilar murmurs may signify congenital diseases like aortic stenosis or pulmonary stenosis. A continuous murmur at the base usually indicates a patent ductus arteriosus (PDA).


To summarize, several factors should be considered when encountering a murmur in a patient. While we’re always available to discuss individual cases before considering referral, here are a couple of key pointers for further assessment:

  • Any murmur above grade 2 in a young animal
  • Basilar murmurs
  • A murmur of grade 3 or higher at the left apex in an older small breed dog
  • A murmur with a gallop rhythm in a cat
  • A continuous murmur
  • Any right-sided murmur
  • Any murmur accompanied by clinical symptoms indicative of heart disease

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