A heart murmur is a whooshing or swishing sound heard during a physical exam, distinct from the normal rhythmic heartbeat. This extra noise is caused by turbulent blood flow moving through the heart’s valves or chambers. Determining whether a heart murmur is hereditary is complex, as the sound itself is a physical finding, not a diagnosis. The answer depends entirely on the underlying cause, which can range from a temporary, harmless increase in blood flow to a serious, inherited structural heart condition.
Understanding the Types of Heart Murmurs
Heart murmurs are broadly categorized into two distinct types: innocent (or functional) and pathological (or abnormal). Innocent murmurs are extremely common, particularly in children, with up to 80% experiencing one at some point. These are the sounds of blood flowing normally through a healthy heart at a faster-than-usual rate.
Innocent murmurs are not linked to structural heart problems and are never hereditary or serious. They often disappear as a child grows but can occur temporarily in adults due to conditions that increase blood flow, such as fever, exercise, or pregnancy. Pathological murmurs, in contrast, indicate an underlying structural issue, such as a valve problem or a hole in the heart wall. Only pathological murmurs may have an inherited component.
Inherited Causes of Heart Murmurs
A pathological heart murmur can be the first indication of an inherited heart condition affecting the heart’s structure. These conditions involve the inheritance of an underlying genetic defect that causes turbulent blood flow, not the sound itself. Many congenital heart defects (CHDs) cause murmurs and have a significant genetic component.
Most CHDs are multifactorial, arising from a combination of genetic and environmental factors, but specific defects have clearer inheritance patterns. For example, septal defects, often called “holes in the heart” (like VSDs or ASDs), can be inherited. A bicuspid aortic valve, a condition where the aortic valve has two leaflets instead of the usual three, often runs in families.
Genetic syndromes affecting connective tissue can lead to murmurs by weakening heart structures, particularly the aorta and valves. Marfan syndrome, for instance, can cause the aortic valve to enlarge, leading to a murmur from blood flowing backward. Hypertrophic cardiomyopathy (HCM) causes the heart muscle to thicken, which obstructs blood flow and creates a murmur. Mitral valve prolapse, a condition causing a murmur, may also have a genetic basis.
Non-Inherited Causes and Acquired Conditions
A pathological heart murmur does not automatically imply a genetic risk, as many are acquired later in life. In adults, abnormal murmurs are frequently related to heart valve damage that develops over time. Calcium deposits, which accumulate with age, can cause the heart valves to become stiff and narrow, a process called degenerative valve disease.
Infections are a common cause of acquired murmurs, such as endocarditis, an infection of the heart’s inner lining and valves. Historically, rheumatic fever, a complication of untreated strep throat, was a major cause of acquired murmurs by damaging the heart valves, a condition known as rheumatic heart disease.
Conditions that temporarily increase blood flow, such as anemia, an overactive thyroid gland, or high blood pressure, can also cause pathological murmurs that are not inherited.
When to Seek Genetic Counseling
If a heart murmur is diagnosed, especially a pathological one, a thorough evaluation of personal and family medical history is the next step. This involves a cardiologist or genetic counselor gathering information, often looking back three generations for any history of heart defects, early-onset heart attacks, or sudden unexplained deaths. Diagnostic testing, such as an echocardiogram, is used to visualize the heart’s structure and confirm the cause of the murmur.
If an inherited heart disease is suspected or confirmed, genetic counseling is recommended for the patient and their first-degree relatives. First-degree relatives (parents, siblings, and children) have a 50% chance of inheriting a single-gene variant that causes a heart condition. Genetic testing can identify a specific mutation, allowing for targeted screening of asymptomatic family members. This proactive approach helps determine who is truly at risk and allows for earlier intervention to prevent serious complications.