OPINIONS WANTED!!!

It's it accurate to go by the heart rate to determine girl or boy? At my ultrasound the baby's heart rate was 172 and at my appointment today the doctor said it was in the 160's I know lower heart rate means boy and higher heart rate means girl but is it just a myth? Are there any moms out there that had baby's boys but their heart rates were still high? My boyfriend really wants a boy so was kinda disappointed when the doctor told us the heart rate need advice