Phacoemulsification apparatus includes a phacoemulsification handpiece having a needle and a power source for ultrasonically vibrating said needle and a pulsed electrical power source for providing pulsed electrical power to the handpiece. Irrigation fluid is provided to the handpiece needle and aspirating fluid is removed from the handpiece needle. Input means enable the surgeon to manually control pulse amplitude, and control means in response to a selected amplitude determines a duty cycle of the provided pulsed electrical power. An off duty cycle is controlled to ensure heat dissipation before a subsequent pulse is activated
