it depends on person's health condition. athletes have low heart rate bacause their hearts are very strong, they can pump out enough blood for their bodies' need. most people need to have over 60 to provide enough blood.
i didn't know my heart rate until i checked. the reason i checked was i was suffering server short breath, lack of energy (i literally could not talk). it is not fun. however, i walked little and it helped increasing my heart rate and i feel much better. i believe light exercise should fix my problem. not cardiologists for sure.