Hypothyroidism. Anything much below 70 is indicative of suppressed metabolism. Up towards 90 is actually best. There are clear correlations between health, intelligence, and resting heart rate. The most intelligent people have resting heart rates up around 95 bpm.

The idea that a lower pulse rate is better comes from the observation that endurance athletes have low resting pulse rates, and it is generally assumed that endurance exercise is healthy. The truth is that high volume exercise suppresses the metabolism and compromises health.

Can you offer a reference for this claim?

Here's a counter-claim: "A normal resting heart rate for adults ranges from 60 to 100 beats a minute.

Generally, a lower heart rate at rest implies more efficient heart function and better cardiovascular fitness. For example, a well-trained athlete might have a normal resting heart rate closer to 40 beats a minute."

Source: Mayo Clinic, http://www.mayoclinic.org/healthy-living/fitness/expert-answ...