Extra Heart Sounds (S3 and S4) Summation Gallop at 120 beats per minute - waveform Lesson Waveform Video play pause Maneuver:Supine Position:Mitral Chestpiece:Diaphragm Table of Contents Introduction Third Heart Sound Gallop Fourth Heart Sound Gallop Third and Fourth Heart Sound Gallop Summation Gallop at 120 beats per minute At a heart rate of 120 beats per minute, the diastolic period is shortened. This causes the third and fourth sound to be superimposed, creating a single loud sound.The anatomy tab shows an enlarged left ventricle with decreased left ventricular contractility and a minimally enlarged left atrium.