A murmur is a sound heard by the physician when he or she listens to the heart with a stethoscope. The sound may be caused by an abnormal heart structure such as a narrowed valve that creates a murmur as the blood flows through a smaller than normal area. This represents a pathologic murmur because the turbulent blood flow is caused by a structural defect in the heart. Patients with these murmurs have to take antibiotics before invasive procedures to prevent infection of the heart and must be followed by their respective physicians to receive appropriate medical care.

In contrast to a pathologic heart murmur, as many as 80% of children will have an innocent or functional murmur at some point in their lives. This type of murmur arises when blood flow becomes turbulent due to an increase in blood volume or velocity as it flows through normal heart valves and blood vessels. Innocent murmurs are heard in patients with fevers, elevated levels of thyroid hormone or after physical exertion when the heart is working harder than it usually does to pump blood to the rest of the body.

A physician considers a number of factors when listening to the heart to discern an innocent from a pathologic murmur. Some of the important things to evaluate are described below.

 The timing of the murmur in relation to the “lub-dub” heart sounds is important. Most innocent murmurs are heard when the heart muscle is contracting and very rarely are they heard when the heart is relaxing. Therefore, a murmur heard when the heart is relaxing should be investigated further.

 If the patient is experiencing physical symptoms such as chest pain, shortness of breath, dizziness, cyanosis (turning blue) or excessive fatigue with minimal activity then the murmur should be investigated further.

 If the murmur is loud in its intensity or accompanied by a palpable tremor over the chest wall, it should be investigated further.

 If the heart sounds are irregular, the murmur should be investigated further.

 Innocent murmurs heard when the heart is contracting often decrease in intensity when the patient stands because there is a decrease in the amount of blood returning to the heart and less turbulent flow.

 Patients with innocent murmurs have normal heart sizes on chest x-ray as well as normal electrocardiogram findings.

As described above, innocent murmurs are the result of “noisy” blood flow through a normal heart and cause no adverse health effects. They are very common, often transient in nature and should be distinguished from a pathologic murmur.

Additional Notes:
Frank, Martin J, Sergio Alvarez-Mena and Abdulla M. Abdulla. Cardiovascular Physical Diagnosis. Year Book Medical Publishers. Chicago. 1983. pp 242-27.

Park, Myung K. Pediatric Cardiology for Practitioners. 4th ed. Mosby. St. Louis. 2002. pp 30-33.