Just a fun aside: in my 20s, I observed my heart rate at various times everywhere from the low 40s to 200 and once at 0. (For about 10 seconds, then I hit the floor flat on my back and my heart restarted. Previous to that I had full line voltage running from one sweaty hand to the other while standing on a step ladder.)

I highly recommend keeping the resting heart rate in 2 digit range. It took me a full 24 hours to recover from that that short spell at the lower number.

Ben