Veteran pop-rocker Elton John underwent heart surgery in a London hospital Friday (July 9) to have a pacemaker implanted, according to the Associated Press and Reuters. The surgery was successful and John was released Saturday, the reports said. The pacemaker is intended to correct what John was quoted as calling "a minor imbalance in my heart." The singer, who has canceled several recent concerts due to the problem, reportedly intends to resume live performances as soon as next month. John's "Candle in the Wind 1997" is the best-selling single of all time, and he has been cited as an influence by artists ranging from Axl Rose to Ben Folds.