Abstract: The system coordinates the speed of a blood pump, in an extracorporeal blood circuit for a patient, with the blood flow from the patient to pass the blood through a treatment device such as an oxygenator and then back to the patient. The blood from the patient flows through a bladder which actuates a transducer to control an integrator and current amplifier. The current amplifier charges a capacitor to the breakdown potential of a DIAC avalanche diode causing the diode to fire and dump the charge of the capacitor into a silicon controlled rectifier which energizes the pump motor. The speed of the motor depends on the charging time of the capacitor in response to a signal voltage from the transducer. The motor is stopped by a comparator and flip flop when the blood flow through the bladder drops to a predetermined low value. The speed of the motor may also be controlled manually by a potentiometer.