Heart Murmur by Frank Utchen, DVM

Dr.Utchen, the vet says my dog has a heart murmur. What exactly is this, and is this serious? 

Answer: Heart murmurs can be completely harmless or can represent more serious problems. What a “murmur” refers to is the sound blood makes when is goes through an unusually narrow opening inside the heart.  

In most cases this means a valve is not sealing completely when it is closed and therefore some blood can leak through a narrow defect in a valve that is otherwise supposed to be shut. This can be a condition that is present from birth with no ill effects. A dog can also be born with several heart abnormalities that can result in heart failure at a young age. Finally, a heart murmur can be a result of a heart problem that starts later in life and can get progressively worse over a short or a long period of time.  

One cause for heart murmurs in older dogs is damage that can occur to the heart valves when bacteria flow through the bloodstream. This is not a normal circumstance and the most common cause for this is the entry of bacteria into the blood stream from infected gum tissue in the mouth when dental tartar builds up. If this is the case, your dog should be evaluated to determine whether a teeth cleaning can safely be done. 

The answer to your question hinges on those factors and others, such as the stage of the condition that your dog is presently at. A chest X-ray and heart ultrasound exam are required to determine exactly what the problem is and what, if anything, should be done about it.  

There are several different medications that are used to manage this kind of condition when necessary. Your veterinarian can explain the purpose and effects of these medications.  

Interestingly, studies have repeatedly shown that using heart medications in a dog with a heart murmur, but who has no outward signs of a problem yet (no coughing, no listlessness, no heavy breathing) has no preventative benefit. This is one of the few medical problems where early therapy—prior to the development of outward signs of disease—does not help prevent the progression of the problem. 

The best recommendation for a dog with a heart murmur (who is showing no evidence that it is affecting the efficacy of the heart beats) is to perform a routine set of blood tests to be sure the heart is supplying the body with adequate blood flow, and take an X-ray and perform an ultrasound exam to obtain a baseline set of data so that future X-rays and ultrasound exams can effectively monitor any progression. However, it is not recommended that your dog begin medication until such time as the above outward signs begin occurring.  

Various medications that are used include diuretics like Lasix (furosemide) which cause increased urination and thereby help prevent fluid buildup that can occur in the lungs; Enalapril or Benazepril (medications that improve blood flow out of the heart); and a newer medication called Pimobendan. There are other medications for use in specific situations, but those are the primary drugs employed.  There are low-salt dog foods that are also recommended that your veterinarian can suggest.