Cardiologists have accused a small drug company of withholding data from a clinical trial showing that the company’s drug, meant to reduce the risk of heart attacks, increased the risk instead.

The cardiologists said that the company, Anthera Pharmaceuticals, did not turn over data to academic investigators, as it was required to do, for more than a year.

“Despite a contract that required transfer to the academic authors, the company stonewalled every attempt to acquire the data,” Dr. Steven Nissen, a cardiologist at the Cleveland Clinic, said in an email on Tuesday.

Dr. Nissen was the senior author of a report on the data that was published online Monday by The Journal of the American Medical Association and presented at the annual meeting of the American Heart Association in Dallas. In unveiling the results there, the lead investigator, Dr. Stephen Nicholls, publicly admonished the company.