YORK COUNTY, Pa. (WHTM) – Republican U.S. Senate candidate Mehmet Oz spoke to the York Rotary Club on Wednesday where he faced questions regarding his opponent and ads targeting him.

The disturbing and powerful television ad from a Democratic Super PAC suggested that Oz killed puppies as part of medical research.

“You should know these accusations, not only do they have no validity, but whatever research was being done must have helped humans at some level,” said Oz.

The report that the commercial is based on alleges Oz was part of the team at Columbia University that did research on animals between 1989 and 2010, which allegedly killed hundreds of dogs and left the university fined.

When pressed if he was involved in the research, Oz said he’s the head of the institute and that his name is on many of the forms, but “at no point did I go and do any of the things they’re claiming to dogs. In fact, there’s no evidence that I did and there’s no evidence there’s any settlement. It’s completely manufactured”

Oz’s visit came as his opponent John Fetterman released a letter from his doctor saying the Democrat nominee was fit to serve after suffering a stroke in May.

“Overall, Lt. Governor Fetterman is well and shows strong commitment to maintaining good fitness and health practices,” said Clifford Chen, MD at UPMC. “He has no work restrictions and can work full duty in public office.”

“Since my stroke five months ago, one of the best parts of this campaign has been the unbelievable number of Pennsylvanians who have shared their own stories with us about the major health problems they’ve faced and overcome in their lives,” said Fetterman. “It reminds me why I’m fighting to slash health care costs and make it so every Pennsylvanian can spend more time with the people they love. Unfortunately for Dr. Oz, I’m ready to serve and continue to get better every single day.”

“I’m not worried about John’s health thankfully now,” said Oz after the letter was released. “I’m worried about what’s going on in his head in terms of his ideas, the radical positions that he’s taken.”

Oz and Fetterman will meet for their only scheduled debate on October 25 at 8 p.m. in the abc27 studio in Harrisburg. The debate will be available to watch on air and online in all of Pennsylvania’s 67 counties.