This study examines the heart and its activity in the mite Varroa destructor. Through light microscopy, the duration and frequency of the beat of the mite's heart, which is located over the synganglion, was recorded and analysed. The heart measured 165 µm by 60 µm, and consisted of two lateral trunks, inducing pulses with an average duration of 10 sec and an average frequency of 0.13 Hz. The use of cardiac activity as a new bioassay for accurate assessment of the effect of varroacide compounds was also examined.