The relation between heart activity and locomotor behavior was studied in tethered blowflies (Calliphora vomitoria) by simultaneous recording of the electrocardiogram and the electromyogram. Motor activity resulted in an inhibition of forward beating of the heart. In the case of visual stimulation by movement of black stripes, this inhibition anticipated the motor activity. When this visual stimulation was repeated, motor and cardiac responses waned, but optocardiac response remained present a long time after the disappearance of the optomotor response. These results support the hypothesis of the participation of cardiac activity disturbances in preparatory processes for motor activity in insects.