It's not really a cheat. At night, when you see a hooker on the street, pull up next to her on the sidewalk. She'll stand next to the car like she's talking to you for a little bit, and then she'll get in. You have to drive into a secluded alley or behind some trees, and the car will start rocking back and forth and your health will go up and your money will go down a little bit. But when she's done, you can just get out and kill her and get all of your money back anyway, so its a quick way to build your health back up if you're hurt.