I am 49 years of age,, always kept very fit. I have just had a pace maker put in after my heart stopped on 3 separate times on the one day. There was some one present each time so I am not sure if it would have restarted without intervention or not. I got absolutely no warning or symptoms prior to any of the incidents and felt reasonably well after each. I have been told whilst not common it is not totally unusual in people with a history of intense physical training.