A Texas heart surgeon whose practices recently have been the subject of stories by ProPublica and the Houston Chronicle filed a lawsuit this week against the news organizations alleging defamation.

Dr. O.H. “Bud” Frazier brought the suit in Harris County (Texas) District Court, challenging a May story that examined concerns with the doctor’s conduct, as well as one last month addressing criticism of the first article. The suit also names the stories’ authors, reporters Charles Ornstein of ProPublica and Mike Hixenbaugh of the Chronicle, as defendants.

Frazier, a famed heart transplant surgeon at Baylor St. Luke’s Medical Center and the Texas Heart Institute, asserts that the articles included errors and misleading statements “calculated to falsely portray Dr. Frazier as an inhumane physician.”

“We have seen the complaint in this case, although we have not yet been served,” said Richard Tofel, president of ProPublica. “We think the lawsuit lacks merit, and we intend to defend it vigorously.”

Nancy Barnes, executive vice president and editor of the Chronicle, said: “The Houston Chronicle stands behind the reporters on this story, and our journalism, and we will defend our work vigorously.”

The articles involving Frazier were part of a larger series, “Heart Failure,” jointly reported by ProPublica and the Chronicle.

The first article about Frazier, the transplant program’s founding surgeon, revealed that he had been accused of violating research rules and skirting ethical guidelines. A hospital investigation found that Frazier and his team implanted experimental heart pumps in patients who didn’t meet medical criteria for clinical trials. The findings were viewed as serious enough that St. Luke’s reported the research violations to the federal government and repaid millions of dollars to Medicare.

In his lawsuit, Frazier calls the decision to repay the money “ill-advised” and criticizes St. Luke’s findings of research violations. He also says that he was motivated by saving lives, not by money.

Other stories in the series detailed how St. Luke’s heart transplant program has in recent years performed an outsized number of transplants that resulted in deaths or unusual complications.

St. Luke’s temporarily suspended heart transplants in June to review two recent patient deaths; it reopened the program two weeks later. Medicare has since announced that it intends to cut off funding for St. Luke’s heart transplant program in August, citing shortcomings that have not been corrected.