A mechanical CPR device includes a back plate, a first tower removably attached to the back plate, a second tower removably attached to the back plate, and a beam releasably connected to each of the first tower and the second tower. The first tower can include a first linear motion device. The second tower can include a second linear motion device. Each of the first and second linear motion devices can be configured to move one end of the beam toward and away from the back plate. The first and second linear motion devices can be configured to operate in concert such that, when the back plate is resting on a surface, the beam remains substantially parallel to the surface during movement of the beam toward and away from the back plate.