Heidnik was born on November 22, 1943, to Michael and Ellen Heidnik, and was raised in the Eastlake suburb of Cleveland, Ohio. He had a younger brother, Terry. His parents divorced in 1946. The Heidnik children were then raised by their mother for four years, before being placed in the care of their father and his new wife. Heidnik would later claim that he was often emotionally abused by his father. He suffered a lifelong problem of bed wetting, and claimed his father would humiliate his son by forcing him to hang his stained sheets from his bedroom window, in full view of their neighbors. After his son's arrest, Michael Heidnik denied that he abused his son.