Tampa General Hospital officials say staff mistakenly started performing a cardiac catheterization on the wrong patient. The man was not harmed.

Hospital spokesman John Dunn says staff members failed to follow proper hospital protocol to identify the patient before the medical procedure. The hospital is conducting an internal investigation.

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Hospital officials says a doctor "had inserted a catheter and was taking readings, but they hadn't injected any dye."

The hospital did not identify the patient or medical staff involved.

The patient was sedated, but not under anesthesia; it is being reported by Tampa Bay Online.

"We are treating this as a serious incident," Dunn told tbo.com. "We have found the staff involved failed to follow the proper procedures for patient identification."

Dunn said the staff spoke to the patient to explain what happened and to apologize, and the man was later discharged. He is still receiving treatments from his doctor at Tampa General.

A cardiac catheter is a thin plastic tube, which is inserted into an artery or vein in the arm or leg, according to the American Heart Association’s Web site.

The test measures blood pressure within the heart and how much oxygen is in the blood, according to the Web site.

Catheters are also used to inject dye into the coronary arteries, the Web site said, but Dunn said no dyes were injected into the patient.

The Associated Press contributed to this story.