Side effects of Metformin

My husband went in for a full knee replacement. The week before, we want to his endocrinologist and cardiologist to get cleared for surgery. As the surgery was completed and the last staple was placed, my husband went into cardiac arrest. It took 8 minutes to revive him. When he was doing better and about to be released from the hospital, the doctor changed his medication, saying that the Metformin damaged his heart. Has anyone experienced this or heard about this?