When a doctor listens to a baby’s heart, they listen for the regular “lub-dub” sounds of the heart valves opening and closing. A heart murmur is an extra sound—a whooshing, humming, or swishing noise—created by the turbulence of blood flow within the heart or major blood vessels. While hearing this finding can be concerning, murmurs are remarkably common in early childhood. The vast majority detected in babies are categorized as innocent, meaning they are the sound of blood moving through a structurally healthy heart. These harmless sounds are not indicative of a heart defect and require no treatment. A pediatric cardiac evaluation focuses on differentiating this benign sound from one suggesting a serious underlying condition.
What Defines an Innocent Heart Murmur
An innocent, or functional, heart murmur is a temporary acoustic phenomenon produced by the normal, rapid movement of blood through a child’s heart. These murmurs are not caused by structural abnormalities, such as a hole or a narrow valve. The sound often results from blood flowing faster than usual, perhaps due to increased heart output. A child with a fever, anemia, or high excitement may temporarily exhibit a louder murmur because the heart is pumping a greater volume of blood quickly.
One of the most frequently heard innocent murmurs is Still’s murmur, characterized by a distinctive low-pitched, musical, or vibratory quality. This sound is typically heard best along the lower left side of the sternum during the heart’s contraction phase (mid-systolic). A defining feature is sensitivity to a change in the baby’s position or activity. For instance, the sound may become softer or disappear completely when the baby sits up.
Another common type is the pulmonary flow murmur, generated by blood flowing into the pulmonary artery. In newborns, peripheral pulmonic stenosis is sometimes heard, caused by the relatively small size of the pulmonary arteries. This sound typically resolves on its own within the first few months of life as the vessels mature. Most innocent murmurs fade away entirely by the time a child reaches adolescence.
Observable Signs Indicating a Serious Issue
A pathological murmur, caused by an underlying heart defect, is often accompanied by visible symptoms signaling the heart is struggling. The most alarming sign is cyanosis, a bluish tint to the baby’s skin, lips, or nail beds. This coloration indicates that the blood is not being adequately oxygenated due to poor blood flow through the heart or lungs.
Signs of poor cardiac output or heart failure often manifest during exertion, such as feeding. A baby with a significant heart defect may exhibit an inability to complete a feeding without frequent rest breaks (feeding difficulty). This is often accompanied by excessive sweating, especially around the head and face, as the baby expends energy trying to feed. Poor calorie intake leads to failure to thrive, meaning the baby does not gain weight at the expected rate.
The baby’s breathing pattern offers another important clue. Rapid, shallow, or labored breathing (tachypnea) signals that the lungs are struggling, often due to fluid buildup or inefficient heart function. Lethargy or unusual sleepiness is also a warning sign that the heart is not meeting the body’s metabolic needs. Any combination of these symptoms warrants immediate evaluation by a healthcare provider.
Diagnostic Tools Used in Evaluation
If a doctor suspects a structural problem or the baby exhibits concerning symptoms, the child is referred to a pediatric cardiologist for specialized testing. While the initial evaluation includes a physical examination, advanced imaging is required to view the heart’s anatomy in detail. The primary diagnostic tool used is the echocardiogram, or “echo.”
An echocardiogram is a non-invasive ultrasound that uses sound waves to create moving images of the heart’s chambers, valves, and major blood vessels. This allows the cardiologist to visualize the heart’s structure and function in real-time. The echo identifies the precise location and nature of any defect, such as a hole or a narrowed valve, confirming whether the murmur is caused by a structural problem or normal blood flow.
Two other common non-invasive tests provide supplementary information. An Electrocardiogram (ECG or EKG) measures the heart’s electrical activity, revealing abnormal rhythms or signs of strain on the heart muscle. A Chest X-ray offers an image of the heart and lungs, indicating if the heart is enlarged or if there is fluid congestion in the lungs, which are secondary signs of heart failure.
Treatment and Long-Term Outlook
If a baby is diagnosed with an innocent murmur, no treatment or activity restrictions are necessary. The heart is normal, and the sound will likely disappear as the child grows. When the murmur is pathological, the focus shifts to managing the specific underlying structural defect.
The therapeutic approach varies widely depending on the severity and type of congenital heart defect. Smaller defects, such as a small ventricular septal defect (a hole in the heart), may close spontaneously over time. These require only watchful waiting and regular monitoring by a cardiologist. If the defect causes symptoms like fluid retention or poor heart function, medication may be prescribed, such as diuretics or drugs to improve the heart’s pumping ability.
For more serious defects that do not resolve naturally, intervention is necessary. This may involve a catheter-based procedure, where thin tubes are threaded through blood vessels to repair blockages within the heart. In other cases, open-heart surgery is required to repair complex defects, such as replacing a faulty valve or patching a large hole. The long-term outlook for most children with congenital heart defects has improved significantly, allowing them to lead healthy, active lives.