normal heart rate
is between 60 to 100 beats per minute. you are bradycardic. The reasons for this can be a few different things. Very possible for you is a conduction disorder or block. A heart rate of 40-45 suggests that either your AV node or your purkinje fibers are what are firing your heart to contract when normally it is the SA node.
Of course the only way to know for sure what I am saying is accurate is for you to get an EKG (ECG).
At 81, normally one would assume a pathologic reason as like I described above. The only way to know for sure is to do a complete history on you as well as a physical exam, which over the internet is difficult.
My best advice for you (or the person whom you are referring to) is to go to the doctors and have them check it out. It merits investigation by a clinician.