A Lancashire window cleaner followed a severely disabled woman home and sexually assaulted her before he returned the next day and raped her.
Andrew Richardson, 31, of Thornton Road, Morecambe, was jailed indefinitely on Wednesday for public protection after he admitted taking advantage of his "extremely vulnerable" victim who he met on Morecambe promenade.
Sentencing at Preston Crown Court, Judge Norman Wright said the defendant took advantage of his victim as he subjected her to an "appalling and horrific" ordeal.
Richardson pleaded guilty to rape and sexual assault at an earlier hearing but initially lied to detectives that sex had been consensual between the pair.
Duncan Birrell, prosecuting, said the woman, in her 50s, had been out walking her dog on June 18 when Richardson approached her and struck up a conversation.
"The prosecution say that it would have been immediately obvious to the defendant that she was vulnerable," he said.
He exposed himself to her and then followed her home where he effectively forced himself in and then sexually assaulted her.
Richardson went back to her home the next day and again put his foot in the door as she opened it.
He went on to rape her and the ordeal only stopped when the woman's care support worker called in.
Richardson lied that he was a relative and left the address before the victim was found upstairs in her bath.
Michael Hayton, defending, said his client had lived a good life until the collapse of his relationship with his long-term partner and mother of his child.
He lost his job as a manager at an estate agent in Morecambe through heavy drinking and had then set up his own window cleaning business.
His pre-sentence report said the defendant had only shown a superficial understanding of what he had done and did not fully appreciate the effects of his actions.
Mr Hayton said although the offences were "extremely serious" they could be treated as "a one-off" as he argued for a determinate sentence.
Judge Wright disagreed and said Richardson should serve at least four years behind bars before he could be considered for parole.
Addressing the defendant, he said: "These are serious matters.
"They were horrific and appalling.and can provoke nothing but utter revulsion from anyone learning what you did."
He concluded that the absence of information on what triggered the offences meant he could not be satisfied that Richardson posed no significant risk to the public in future.
Richardson also pleaded guilty to stealing a small amount of money from the woman on June 18 and was given eight months in jail, to run concurrently.