Various techniques, surgical as well as electrophysiological, have shown the myocardial activity of insect hearts, including the house fly, to be variable (Ballard and Holcomb 1965, Ballard and Hall 1969, Jones 1964). To study this problem further, surface potentials, recorded by means of suction electrodes placed on 2 segments of the heart of the house fly Musca domestica L., were compared. Simultaneous recordings suggest an anterior influence on the heart beat, as well as a possible cause for its variability.