A Cardiac Pulmonary Resuscitation (CPR) device (CPD) for performing CPR on a patient (PT). A supporting structure (L1, L2, F) with two legs (L1, L2) shaped to accommodate space for the patients (PT) thorax between them. The legs (L1, L2) have clamp mechanisms (CL1, CL2) to allow clamping onto a backboard (BB). A compression box (CB) with a plunger mechanism (PM) with a contact pad (CP) projecting downwards from the enclosure (CS), and a processor (P) for controlling the plunger mechanism (PM) to perform CPR on the patient (PT) in an automatic manner. A height adjustment mechanism (H) is used to fix a height (h) of the compression box (CB) relative to the supporting structure (L1, L2, F). The height adjustment mechanism (H) can allow the compression box (CB) to move in relation to the supporting structure (L1, L2, F) in a first operating state, by help of gravity. Hereby, the compression box (CB) can enter a height (H) where the contact pad is in contact with the patients (PT) chest, preferably within a predetermined contact force range, upon clamping of the supporting structure (L1, L2, F) onto the backboard (BB). Hereby, the height and contact force parameters are inherently set automatically by the device, when the operator has clamped the CPR device (CPD) onto the backboard (BB). This setup task is easy for the operator, time without CPR can be saved, and CPR can be initiated with a correct contact force.
