Abstract: Apparatus, adapted for use in explosive as well as nonexplosive atmospheric environments, for alternately applying intermittent compression to the legs of a patient during surgery, postoperative recovery periods and other periods of muscular inactivity to accelerate venous blood flow in the lower extremeties and inferior vena cava and thereby prevent blood clotting in these vessels. A pair of double-walled pneumatic leggings adapted to extend from the ankle to the knee of the patient are provided for fitting on each leg. Each legging is connected by a separate conduit to a non-electrical regulating and timing control circuit adapted to receive compressed air, oxygen or other pressurized gas from any available source and transmit it by means of periodic intermittent pulses alternately to each legging.