Hôtel-Dieu Grace Hospital officials said Wednesday that Dr. Barbara Heartwell, shown here in October 2009, performed a mastectomy on a patient who did not have cancer. (CBC)

Hôtel-Dieu Grace Hospital in Windsor, Ont., is investigating what it calls a serious mistake involving a woman who had a mastectomy when she did not have cancer.

The hospital held a news conference Wednesday afternoon explaining details of the incident.

Hospital officials said the woman was initially told she had breast cancer and underwent a single mastectomy in the fall of 2009.

The operation was performed by Dr. Barbara Heartwell, a surgeon with 28 years of experience.

It was only after the surgery that Heartwell told the patient she had made a mistake, and that the woman did not have cancer.

'Humans are not infallible and mistakes do unfortunately occur.' —Warren Chant, hospital CEO

The hospital said Heartwell had misread a pre-surgery pathology report that ruled a lump in the woman's breast was benign.

A release issued by the hospital said that after misreading that report, Heartwell "unfortunately proceeded with the surgery."

Media call prompts investigation

The hospital said Heartwell notified the chief of her department about the error earlier this year, but the hospital administration only became aware of the incident after receiving a call from the media on Feb. 5.

Hôtel-Dieu Grace Hospital said it immediately contacted Heartwell and reached out to her through the hospital's patient advocate.

"We are profoundly sorry this has occurred," said Egidio Sovran, chair of the hospital board.

"While errors are extremely rare, as a hospital we take every possible precaution to ensure the highest level of care, and will be conducting a full investigation."

The hospital said it is reviewing all of Heartwell's past mastectomy patient records.

"Humans are not infallible and mistakes do unfortunately occur," said Warren Chant, CEO at the hospital. "We appreciate how difficult this is for the patient and her family ... and will continue to reach out to assist this patient."