Just had a good piece of work with Dove but still failed to get her heart rate up above 126 bpm (right hand graph) and Frog ( max HR 198 bpm) We went around the circular gallop twice, As I was trying to get Dove's HR up I tried to do some sprint work with her and got to a maximum speed of 37.4 mph (12 secs per furlong) with an average of 15 secs/fur . I was too scared to go around the bends at that pace so had to take a pull. Then up the long uphill gallop at a good clip (18 secs/fur). Probably should have gone up again but there was another string behind us and Frog was getting rather silly. Anyway, the bottom line is that fast work on the flat doesn't seem to elevate the HR (in Dove's case.) Her recovery rate was 50 after 2 mins. (Frog's 113 bpm) In a race situation she will have a much higher HR and that is when you could run the risk of lactic acid build up but as we don't want to work her too hard at home and risk injuring her we may have to race her as a piece of work. Although Frog's HR seems rather high in comparison you have to bear in mind that as a horse gets older the HR becomed lower, also Frog has an unconditioned heart as she has only been broken in for a short while and she is still not completely relaxing, particularly after a piece of work which is why her recovery rate is still very high.