I Was Just Prescribed Metoprolol Tartrate, 25 Mg, 1/2 Tablet

I was just prescribed Metoprolol Tartrate, 25 mg, 1/2 tablet PO every 12 hours. AND was warned it lowers pulse rate so to monitor and call the doctor if it gets down around 60. I told him my NORMAL pulse is around 60, but since it was 83 in his office, he didn't say anything. So it's close to time for my first dose and I took my pulse manually... 58. Then took it via my BP machine... 52. Do I take it or not?