The bishop with whom he consults does not believe Karras is qualified to perform the rites, and appoints the experienced Merrin—who has recently returned to the United States—to perform the exorcism, although he does allow the doubt-ridden Karras to assist him. The lengthy exorcism tests the priests both physically and spiritually. When Merrin, who had previously suffered cardiac arrhythmia, dies during the process, completion of the exorcism ultimately falls upon Father Karras. When he demands that the demonic spirit inhabit him instead of the innocent Regan, the demon seizes the opportunity to possess the priest. Karras heroically surrenders his own life in exchange for Regan's by jumping out of her bedroom window and falling to his death, regaining his faith in God as his last rites are read.