It’s taken him less time to learn how to be a TV star then it did to finish medical school. Heading into his fifth year as host of “The Doctor Oz Show,” Mehmet Oz, 52, has become one of the most recognized faces on Earth. One of the top cardiothoracic surgeons of his generation is also now the go-to guy for housewives around the world looking to drop belly fat. “I had no interest in this,” says Oz, who, despite a frenzied TV production schedule still sees patients at New York Presbyterian Hospital in Washington Heights on Thursdays, where he does rounds and heart surgeries. For nonurgent cases, th ere’s a three-week waiting list for an appointment with the doctor.