i couldnt help it

so way back when in a previous life i aquired a heart rate moniter. so in the interest of science the girlfriend at the time suggests i wear it whilst we were having sex so she could see how fast she could get my heart going. this was a mistake. seems during copulation my heat rate drops quite a bit. this did not please her. oh no i was accused of not liking sex with her and she took it as a personal affront that my ticker was not on the verge of exploding. what do you do,one cannot control how ones body reacts can one now.