This is a graphic example of normal splitting of S1.
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.