HG - Sometimes strenuous or prolonged exercise can increase the heart rate rapidly like this. In view of the fact that it came down again fairly quickly, I wouldn't worry too much about it. Normally, an individual recognises the increase like this as "palpitations" - which people complain of feeling like a fluttering in the chest, which can be associated with pain on occasion. Alot of people get them (normal healthy individuals) and they aren't only restricted to those who exercise - palpitations can occur due to anxiety, highly stressful situations, having a large meal and a whole load of other reasons. If it happens again though, I'd see your GP and get him to do a check heart tracing to check on the heart rhythm.