Volhard1 in 1905 studied the characteristic sphygmographic features in cases of pulsus alternans and reported that by listening to the heart one could recognize a conspicuous alternation of the second heart sound in all the cardiac cycles and of the first heart sound in only three or four cycles after each extrasystole. This alternation of the sounds revealed itself through modifications in their intensity and pitch; the sounds in the cycle with a large pulse beat were more intense and of a higher pitch than those in the cycle with a small pulse beat.
Although the initial fact was verified at the beginning of the present century, there are only a few cases reported in the medical literature in which alternation of the heart sounds was recognized on auscultation (Meyer and Levy2 and Morris3). With the exception of Morris,3 all other authors who have been interested
COSSIO P, LASCALEA M, FONGI EG. ALTERNATION OF THE HEART SOUNDS. Arch Intern Med (Chic). 1936;58(5):812-824. doi:10.1001/archinte.1936.00170150049004