Heart Murmur - Causes

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What causes a heart murmur?

Functional heart murmur

Many heart murmurs are harmless and referred to as innocent or functional. They are caused when blood rushes through the heart quickly during normal function while no heart disease may exist. There may be an underlying medical condition that can lead to an innocent murmur. These may include situations where the heart beats more quickly such as fever, anemia, hyperthyroidism, and pregnancy.

Congenital heart murmurs

Congenital heart murmurs are heard in the newborn. They may be due to abnormalities in the valves, septae, or arteries, and veins that carry blood to and from the heart. In some complicated heart disease conditions there may be a combination of all three. Many congenital heart murmurs resolve spontaneously without medical intervention while others require surgical operations for repair.

Patent ductus arteriosus (PDA) may cause a heart murmur in a newborn. Prior to birth, the aorta and pulmonary artery are connected by a small artery, the ductus arteriosus, to complete fetal blood circulation. Shortly after birth, this artery is supposed to close. If other congenital heart abnormalities exist, the ductus may remain open to help maintain some blood circulation. Sometimes, when no congenital abnormalities exist, the ductus doesn't completely close and a murmur may exist. Many times the patent ductus arteriosus closes by itself over time. Occasionally, medications or surgery may be required to close off the patent ductus arteriosus.

Valve abnormalities

Abnormalities of the valves of the heart may cause a heart murmur. Any of the heart valves may be affected and clinical symptoms depend upon the severity of the valve damage and whether the blood flow pattern within the heart is maintained. Each valve problem often leads to a specific character and timing of heart murmur.

  • Valve stenosis is narrowing of a heart valve. This often occurs over time as the valve scars due to injury and scarring from infection such as in rheumatic fever or from a congenital birth defect. Calcification of a valve may also result in stenosis. This causes the heart muscle to work harder to push blood through the narrowed opening and possible heart failure.
  • Valve regurgitation (or insufficiency) is a valve that leaks causing blood to pass backward against the normal blood flow pattern in the heart. A valve may have both stenosis and regurgitation.
  • Valve sclerosis is the mild narrowing and stiffening of the valve (most often seen in the aortic valve) due to aging. It is associated with atherosclerotic heart disease.
  • Valve prolapse is a bowing of a valve that causes some leaking and most often involves the mitral valve.
  • Endocarditis is an infection of the lining of the heart that may involve and destroy a heart valve. The source of the infection is usually elsewhere in the body and it travels via the bloodstream to infect the heart. Most often, there is a previous underlying heart condition.

Holes in the walls of the heart (the septum that divides the heart chambers) can be the source of a heart murmur. Atrial septal defect (ASD) describes a hole in the wall that separates the collecting chamber of the heart while a ventricular septal defect (VSD) affects the wall dividing the pumping chamber.

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Comment from: Julie, 45-54 Female (Patient) Published: May 30

The cause of my murmur was initially mitral valve regurgitation, which was diagnosed right after I gave birth to my 3rd child, at age 27. After several tests it was determined that no treatment was necessary unless the condition worsened. I was recently tested again and the condition morphed into mitral value prolapse, for which I take Bystolic (a beta blocker) to help control the premature ventricular contractions (palpitations). I sometimes still get dizzy and experience chest pain.

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