During the second stage of labour the transducer, which is designed to pick up the signals from the pulsations of fetal heart ventricles (using the Doppler technology), may erroneously pick up signals from the pulsating maternal iliac blood vessels. The expected features on the fetal heart rate (FHR) during the active second stage of labour when the hypoxic stress is maximum include decelerations (due to reduced uteroplacental circulation or umbilical cord compression) or a subacute hypoxic pattern. In contrast, due to pain, and maternal efforts, repetitive, large-amplitude accelerations will be observed if the maternal heart rate (MHR) is erroneously recorded as the FHR. The misinterpretation of MHR artefact as FHR can potentially mask an ongoing abnormal FHR trace, giving the appearance of a falsely reassuring trace. This can lead to increased perinatal morbidity and mortality due to the non-recognition of intrapartum hypoxia or fetal demise in the second stage. The ‘double mountain peak’ sign with high-amplitude accelerations coinciding with uterine contractions should arouse the suspicion of erroneous recording of MHR as FHR.