"Usually CME course directors have some direct knowledge of the body of work done by experts that qualifies them to lecture," said Dr. William O'Neill, who was a cardiologist at Beaumont before becoming executive dean for clinical affairs at the University of Miami School of Medicine. "CME courses themselves do not require background checks or verification of credentials. The AMA [American Medical Association] and ACC were victimized. Somehow this man was able to pass himself off as an expert."
The ACC said it has since severed its relationship with Hamman. The information he presented at this year's annual meeting was peer reviewed and was appropriately accredited, so they say they stand by the material he presented at the meeting.
A Beaumont spokeswoman told the Associated Press Hamman resigned after the hospital checked his credentials and discovered he was an imposter.
While Hamman may be an embarrassment to some of the medical community, others say they are relieved he never did any harm to patients.
"There is no way this guy could have used this ruse to take care of patients (it would have triggered far more serious credentialling)," Dr. Cam Patterson, chief of cardiology at the University of North Carolina Chapel Hill School of Medicine in Chapel Hill, N.C., wrote in an e-mail.
"Fortunately, unlike some other imposters, it appears that he did not put patients directly at risk," said Dr. Alan Kadish, formerly a professor of medicine at Northwestern University's Feinberg School of Medicine.
ABC News' Sharyn Alfonsi and Lee Ferran contributed to this report.