Your baby's gender CANNOT be predicted by heart rate!  Please don't fall for this "old wives tale"; although people (and even doctors) insist on repeating it, it has been disproven by several medical studies. 

Fetal Heart Rate for Gender Prediction

As the old wives' tale has it, if your unborn baby's heart rate is higher, above 140 beats per minute, that means you're carrying a girl. A lower heart rate below 140 bpm means you're having a boy.

It's hard to resist such an easy test, and ever so tempting to over-analyze the pitter patter of that tiny heart. In early pregnancy, the reassuring sound of that heartbeat is just about the only thing we've got to show a baby's even there.

But don't get your hopes up, or have your hopes dashed, based on your baby's heart rate, because it has absolutely nothing to do with what your baby has between its legs. This particular old wives' tale was found to be completely false by a medical study 20 years ago. Another medical study in 2006 confirms that fetal heart rate has nothing to do with the baby's sex, and even more convincing, Maureen has even conducted her own in-womb experiment to prove it.

Full article:  http://www.in-gender.com/Gender-Prediction/Fetal-Heart-Rate.aspx