According to Official Guinness Records,
The longest working pacemaker (present day) belongs to Randy Kasberg (USA) which has been working for 36 years and 337 days, after it was fitted on 30 September 1977 in Gainsville, Florida, USA, as verified on 2 September 2014. After the surgery Randy was told that the only things he couldn't do with the pacemaker were get too close to an car ignition system or radar oven.
For a complete list of 2014 records, please visit 2014 Guinness Records in United States.