What is the main cause of heart murmurs?

Heart murmurs primarily arise from turbulent blood flow, which can occur due to various factors, most commonly including valve defects or conditions that lead to increased blood flow. When blood flows smoothly through the heart valves, it produces a quiet sound; however, when there are abnormalities, such as valve stenosis (narrowing) or regurgitation (leakage), the flow becomes turbulent. This turbulence generates additional noise, which is what's perceived as a heart murmur.

In some cases, certain physiological conditions can lead to high blood flow, such as during periods of intense physical activity or in special situations like pregnancy, contributing to the development of murmurs as well. These factors emphasize that murmurs are not generated from normal, laminar blood flow, which is what would typically occur across healthy heart valves or during normal heart contractions.

The other options — stable blood flow, normal heart contractions, and electrical disturbances — do not result in the sound profile characteristic of murmurs. Instead, they contribute to a normal heart function. Thus, the root of heart murmurs fundamentally lies in the disturbed or turbulent flow of blood caused by structural heart issues or physiological conditions.