St. John's Mayor Dennis O'Keefe was reported to be resting after what officials described as successful surgery to address a blocked artery.

O'Keefe underwent open-heart surgery Wednesday at the Health Sciences Centre in St. John's to clear three blockages identified in a single artery last week. O'Keefe collapsed following a routine stress test, and was revived by CPR and a defibrillator.

Dennis O'Keefe underwent open heart surgery Wednesday in St. John's. (CBC)

"The mayor's doctors have told the family that the surgery went as planned and was very successful," city hall said in a statement.

O'Keefe will be watched closely for the next 48 hours, the statement said.

Deputy Mayor Shannie Duff told CBC News that she was extremely relieved to hear that the surgery had gone well, and that staff at city hall were anxious on Wednesday morning while the surgery was underway.

O'Keefe is expected to be away from his post for between four to six weeks.

"The mayor's family would like to thank the public for their warm wishes and the outpouring of support the mayor has received while in the hospital," the statement said.