The primary function of a pacemaker is to treat slow hearts. The pacemaker will only pace the heart when needed. If your heart is doing well on its own, the pacemaker will simply observe. But if the heart needs a little help the pacemaker will deliver pacing to help the heartbeat normally. The primary function of a CRT-P is to get the chambers of the heart to beat in synchrony. This allows the heart to effectively pump blood to the body.