Former President Bill Clinton underwent four hours of surgery Monday at New York Presbyterian Hospital/Columbia as doctors performed a quadruple heart bypass.

After the surgery, the President’s doctors told reporters that some of the bypassed blood vessels were 90 percent obstructed and that without the surgery Clinton would have suffered a “substantial” heart attack in the future.

The 58-year-old former President was wheeled into the operating room on Monday morning after spending the weekend in the hospital.

Clinton’s wife, New York Sen. Hillary Clinton, and his daughter Chelsea were with him throughout the weekend.

Hillary and Chelsea Clinton issued a statement Monday afternoon thanking God, Clinton’s medical team and those who had supported the former President with their prayers and messages.

Dr. Craig R Smith, chief of cardiothoracic surgery at New York Presbyterian, headed the surgical team that performed the operation.

He told reporters Monday afternoon that the procedure was “routine” and that he expected Clinton to leave the hospital within four or five days.

Recovery could take several months and could keep Clinton on the sidelines during the home stretch of the race between President George W. Bush and Massachusetts Sen. John Kerry.

Clinton was taken to the hospital on Friday for tests after suffering chest pains and shortness of breath.

His wife told supporters Friday at the New York State Fair in Syracuse her husband spent Thursday night at home and was admitted Friday after tests confirmed the need for surgery.