Figure 1: A. An oscilloscopic image of high-pitched fetal heart tones recorded on 35 mm film with a photographic camera. The 1.2 kHz oscillation was modulated by the 60 Hz fetal heart sound vibration. B. The sinusoidal FHR existed in the high-pitched heart sound was recorded and realized by the processing of tape-recorded high-pitched tone by a FHR monitor long after its listening. The sinusoidal FHR of fetal heart sound was not detected listening to the high-pitched clear fetal heart sound.