Heart Murmur in Babies: Usually Harmless, but Worth Checking

First-month check-up. The paediatrician keeps the stethoscope on your baby's chest a little longer, then says: "He has a little heart murmur." For many parents, those words are frightening. Yet it describes a simple sound, and in the vast majority of cases that sound hides no disease.

What matters is knowing how the doctor tells a harmless murmur from one that reveals a malformation, which tests may be requested, and which signs should make you see a doctor without waiting.

What is a heart murmur?

It is an extra sound the doctor hears between heartbeats, when blood flows a little turbulently. It is not a disease in itself, but a sign that needs interpreting.

It is extremely common. According to La Revue du Praticien, it is heard in about half of newborns and a third of infants and children. SickKids hospital in Toronto estimates that almost every child has one at some point in life, and that only about one murmur in a hundred signals a heart problem.

Functional or organic murmur: what is the difference?

A functional murmur, also called innocent or non-organic, is a sound produced by a perfectly normal heart. It is by far the most common. SickKids describes it mainly between ages 2 and 6. It has features the doctor recognises, according to La Revue du Praticien:

• it is soft, brief, sometimes "musical";
• it changes with the child's position and the moment of the examination;
• it is heard better with fever, agitation or anaemia;
• it often disappears when the child stands calmly for a few minutes;
• it comes with no other sign.

An organic murmur reflects an abnormality of the heart or the large vessels. In children, it is most often a congenital heart defect, a malformation present from birth, such as a hole in the wall between two chambers of the heart (atrial or ventricular septal defect). These malformations affect about 1% of children, according to La Revue du Praticien. In adults, the Mayo Clinic cites acquired valve problems more often.

Why does age matter so much?

Because the risk of finding a real malformation is higher in very young children. La Revue du Praticien stresses that the probability of diagnosing a heart defect is higher before 3 months, and the EMC cardiology reference insists: a murmur heard in a newborn, including in the delivery room, must never be neglected.

Some murmurs in infants under 3 months are nonetheless harmless, linked to blood speeding up in the arteries of the lungs. But at this age the doctor is more inclined to ask for specialist advice than at age 4, when a murmur is almost always functional. The tests done at birth are described in our article on your baby's first tests. Babies born early also have particular heart follow-up, discussed in our guide to the premature baby.

Which tests may be requested?

It all starts with a careful examination. The doctor asks about the pregnancy, feeding, growth and family history of heart disease. They listen to the murmur in several positions, take the pulses, and look at skin colour and breathing.

If in doubt, they request a heart ultrasound (echocardiogram). It is the key test, according to La Revue du Praticien and the EMC: it shows the structure of the heart, the valves and the direction of blood flow, and pinpoints the cause of an organic murmur. It is painless, uses no radiation, and is done by a paediatric cardiologist, a heart specialist for children. Depending on the case, SickKids also mentions measuring oxygen on the finger, blood pressure, a chest X-ray or an electrocardiogram.

Which signs should worry you?

An isolated murmur in a baby who is well is reassuring. It is the associated signs that raise the alarm. La Revue du Praticien, SickKids and the Mayo Clinic list, in infants:

• difficult breast or bottle feeds: the baby stops often, tires, has to split meals;
• poor weight gain, visible on the growth chart;
• fast breathing at rest, repeated chest infections;
• heavy sweating without effort, for example during feeds;
• blue or grey lips, tongue or nails (cyanosis).

In older children, unusual breathlessness on exertion, fainting or chest pain are added.

What next: what follow-up?

For a functional murmur, nothing. No treatment, no follow-up, no restriction. La Revue du Praticien goes as far as judging it pointless, even harmful, to see the child regularly in paediatric cardiology, because this feeds a worry with no basis. All sports are allowed, including competitive ones, and SickKids confirms that no limit on activity is needed.

For a malformation, follow-up depends on its nature. A small ventricular septal defect may close on its own and need no further monitoring, or be reviewed every 3 to 5 years without restrictions, according to La Revue du Praticien. Other abnormalities need treatment, sometimes surgery, and long-term heart follow-up. Your paediatric cardiologist will give you a precise plan: write it in the health record book and share it with your regular paediatrician. To know which doctor follows what, read our guide to choosing a paediatrician.