Heartstopper (2006)

In a stormy night, the evil serial-killer Jonathan Chambers is executed in the electric chair. The arrogant coroner Doctor Hitchens brings the corpse in an ambulance to a hospital for the autopsy escorted by the County Sheriff Berger that arrested Chambers. Meanwhile the outcast high-school student Sara Wexler tries to commit suicide on the road and is hit by the Sheriff Berger's car. While bringing Sara in the same ambulance that is transporting the body of Chambers to the hospital, the teenager sees the dead coming back to life. In the hospital, Sara shares the room with the stabbed teenager Walter that coincidentally is her schoolmate, and she asks him to help her to leave the hospital. She tells what she saw, but Walter in principle believe Sara is nuts. However, when he sees blood on the corridor, he helps Sara to escape from their room. However, they find that all exits are locked and they are trapped in the hospital while the psychopath is slaughtering the patients and staff looking for Sara.