A chest compression device includes a piston to apply compression to the sternum and incorporates leaf springs simultaneously driven by the piston to apply lateral compression to the thorax during chest compressions. A motor in the chest compression device provides motive power to cyclically extend and contract the piston to provide therapeutic chest compressions. One end of each leaf spring is operably connected to the piston and the other end of each leaf spring is secured to the backboard/base or to a support leg of the chest compression device such that during extension of the piston, each leaf spring is compressed against the device base or leg which causes the springs to flex and provide lateral compression of the patient's thorax in addition to the sternal compression of the piston.