Reduplication means doubling; that is, the sounds still strike the ear, not as a single tone, but as a double tone. Both the first and the second sounds may be reduplicated. The appearance of extra beats is a totally distinct phenomenon.
This subject has received scanty attention. Potain, in a study of 500 hearts, makes the first mention in literature. In a certain percentage of normal hearts, he found a doubling of the first sound at the end of expiration and beginning of inspiration; of the second sound, at the end of inspiration and beginning of expiration. All later observers have agreed as to the accuracy of Potain's observation. But as to the interpretation of the phenomena the theories advanced are as variable as possible.
It seemed at once obvious that the reduplication must have a distinct relation to the respiratory cycle. Acting on this basis, Sibson1 and Barr
PILLSBURY HC. REDUPLICATION OF HEART SOUNDS.. JAMA. 1906;XLVII(26):2148-2152. doi:10.1001/jama.1906.25210260018001i