Hospital Massacre

In 1961, an unpopular boy named Harold Rusk leaves a Valentine's Day card at the home of the beauty Susan Jeremy. Susan and her friend David mock and crumple up the card, prompting an enraged Harold to break into the house and kill David by hanging him from a hatstand.
Nineteen years later, Susan is divorced, has a daughter, and a new boyfriend named Jack. On Valentine's Day, Susan has Jack take her to a hospital to pick up the results of a standard physical exam, which her new health insurance plan has requested. On the way into the building, she is observed from a window by a man in surgical garb. The man strokes a photograph of a young Susan, and sabotages the elevator Susan boards in order to delay her while he kills Dr. Jacobs, the doctor who has her paperwork, which the murderer tampers with. A janitor later finds Dr. Jacobs' body, and has his face dunked into a sink full of acid by the murderer after trying to follow him into a nearby storeroom.
While looking for her doctor, Susan coerces a friendly intern named Harry into getting her results, which Harry notices are abnormal, prompting him to bring them and Susan to Doctor Saxon. The peculiarities of Susan's paperwork (which the murderer further sabotages after killing a pair of laboratory workers) cause Doctors Saxon and Beam to order that she be detained for observation. Harry uncovers evidence suggesting that someone is pulling a "con job" on Susan, but he disappears after promising Susan he will straighten things out. Jack, who had fallen asleep in his car while waiting for Susan, enters the hospital to look for her, only to find her during her first escape attempt and subsequently waits for her after the doctors find and reprimand her. While he waits, he is lured to an empty hospital room by the killer via a phone call, who then beckons him. Behind a curtain, Jack finds the corpse of one of the nurses before the killer decapitates him with an electric orthopedic saw.
The killer places a large box next to Susan's bed, which she opens to find Jack's severed head. Susan flees in terror to get help, eventually being found by Saxon and a nurse, who return her to her room. When she attempts to show them the contents of the box, it contains only a cake. After Susan tells Saxon about Harry's findings, Saxon goes to look over the copies of her paperwork in the archives. She follows him but spots the killer heading to the archives too, armed with a surgical hatchet. Inside the archives, the killer waits for Saxon in the dark and drives the hatchet into his skull as he tries to flee, before disappearing. Susan witnesses all of this while hiding, her claims of there being a killer on the loose are disbelieved and she is strapped to a gurney after being deemed delirious. The staff prepare to perform emergency surgery on Susan. Nurse Dora is ambushed by the killer in an empty corridor, who chases her and injects her with poison. Dr. Beam is subsequently stabbed through the neck from behind a medical screen while observing Susan's x-rays. The killer then abducts Susan and takes her to a vacant operating room. Susan pulls off the killer's mask to reveal he is Harry, who is really Harold Rusk. When Susan asks what he wants, Harold responds, "What I've always wanted. Your heart".
Before Harold can cut her open, Susan stabs him after he is distracted by some patients, and escapes. Susan is pursued to the roof by the wounded Harold, who she sets on fire after spilling flammable liquid onto him during their chase, and sends him plummeting onto the street below. The next day, Susan is released, and reunites with her daughter and ex-husband outside of the hospital.