We now want to focus on the auscultatory events in a patient with an innocent murmur. This is a young man in high school, went out for the athletic team and a nurse did a screening exam, and she she was sure this was an innocent murmur, and why? Well, let us all listen together and see if we can decide if it is an innocent murmur. We’ll listen at the upper left sternal edge, we’ll use firm pressure on the diaphragm, the carotid is there for timing. Everyone listen together and watch breathing as well. [sounds]

We just heard a classic innocent murmur. That murmur is generated across the pulmonary outflow tract in a young person with a vigorous circulation. The murmur is early, early in systole, because it is due to turbulence alone. Remember, it’s in the first third of systole that two-thirds of the blood leaves the ventricle. Now, let’s dissect out what we heard to confirm that. The first thing we heard was the murmur and the second thing we tuned in on was splitting of the second heart sound. Let’s take them one at a time. The murmur was short, so you heard not [sounds], but [sounds], short, an empty space after the murmur before the second heart sound. Mimic that, try it [sounds]. A short murmur due to flow alone. And the second thing we heard was normal splitting of the second heart sound. [sounds] In a patient with a flow murmur, for example, from an atrial septal defect, that second heart sound would likely have been fixed split. In our case, this is an innocent murmur generated across the outflow tract in a young, healthy person.

Murmur Location and Radiation

The murmur is best heard at the upper left sternal edge, or pulmonary area. Note the position of the pulmonary valve in relation to chest wall landmarks. Turbulent systolic flow across the pulmonary outflow tract generates the murmur that is best heard in the second left intercostal space.

Upper Left Sternal Edge Murmur

The murmur heard at the upper left sternal edge is systolic, short, early peaking, crescendo-decrescendo and mid frequency. Murmurs at the upper left sternal edge that occur early in systole typically result from turbulent flow when the majority of blood is ejected from the right ventricle.

Murmur Ventricular Volume Curve

This is a graphic example of an innocent murmur. By simultaneously viewing the ventricular volume curve, we can see that two-thirds of the blood ejected leaves the ventricle in the first one-third of systole. Therefore, the innocent flow murmur due to turbulent flow across the pulmonary outflow tract occurs in early systole.

Upper Left Sternal Edge

The second heart sounds at the upper left sternal edge demonstrated normal splitting and intensity. No abnormal sounds were heard. The combination of an early systolic flow murmur with normal splitting of the second heart sound is consistent with the diagnosis of an innocent murmur.