The initial clinical experience led to further animal research using mongrel dogs at the laboratories of the University of Sydney medical school and at the Royal North Shore Hospital's Wellcome laboratory. In this research measurements were made of electrode impedance and pacing threshold energy over a range of pulse voltages and pulse widths, using intramyocardial electrodes of 10, 20 & 50 square millimeters surface area. The chronic measurements allowed plotting of the relationship between electrode surface area and pulse voltage/width, leading to a conclusion that an electrode area between 10 & 30 mm2 was optimum in terms of energy needed when combined with a pulse width of only 0.5 milliseconds.