Heart beat help

Anyone here who can explain this to me....

I have always had a high resting heat beat, 95-110 bpm even when I was a fit and healthy skinny minnie teenager but I've never had it checked during exercise until half an hour ago. I start at 105 then did 6 minutes of brisk walking and my heart rate fell to 72 bpm. The nurse doing my evaluation just shrugged and said she had no idea. I recently had an echo and no heart trouble was detected so not worried as such but if you need to increase your heart rate to increase health and fitness i'm a bit stumped as to where I stand

Thanks in advance

Cat

sorry stumped! I would perhaps do a bit of exercise again and recheck it and see if its the same!