What did we hear at the lower left sternal edge or tricuspid area? We heard normal splitting of the first heart sound and a normal second heart sound, that is, "didp dub, didp dub, didp dub" - .03 seconds splitting of the first heart sound, a normal observation in this area - first you hear the mitral and the tricuspid component, the mitral is intense enough that it is referred and reflected over here well, so that you can hear it. It is due to first mitral then tricuspid closure, and that due to an asynchrony because of the electrical activation of the ventricle.
Everyone listen together, and note there is no respiratory variation in the first heart sound split. Everyone listen.
Graphic example
This is a graphic example of normal splitting of s1. Let us listen together.
Normal first sound
The normal first heart sound may be single or split. Splitting is due to asynchronous mitral then tricuspid valve closure. The evaluation of first heart sound splitting is of limited diagnostic value, although it may reflect pathology. For example, wide splitting due to delayed tricuspid closure is seen in patients with right bundle branch block. Most important, split first sounds must be differentiated from other acoustic events, for example, a fourth sound and a first sound.