Can't tell gender by heart rate.
You can usually tell gender via ultrasound at 20 weeks.
I have 2 daughters bother if the heart beats were in high 150s. This pregnancy Boy heart rate is 136. Was true for me.
Not an accurate way to detect gender of I may say..my 1st child was always above 160 and came out to be a boy!no second always read 145, 141,150...won't be surprised if it's a boy too.
Old wives tales and it use to be a helpful tip that doctors used too but they threw it out was that if the heart rate was in the high 150's and higher it's a girl.