Different things. It can be normal in a conditioned person (athlete), or it can be caused from pathology in the heart or the thyroid (hypothyroidism) gland. In your age group, the common things are: normally low heart rate due to regular exercise and possibly hypothyroidism; other causes are pretty rare.
Do you? Most common reason to have slow heart rate is athlete's heart from over-training. But what do you mean by slow heart rate? As it still could be normal at your age to have 40 BPM if you are in good shape. Another caveat is: how do you know the heart rate is taken correctly? Sometimes extra beats will not show at the wrist and the count could be artificially low. If you are worried, discuss with md.
Probably nothing. Heart rate varies with respiration normally. It is usually not sensible however. A low heart rate may be a normal occurrence in a conditioned person, however if the low heart rate causes fatigue, dizziness or passing out episodes, it needs to be evaluated. Usually, a treadmill stress test is done to see if the heart rate responds appropriately, if not, the person may need a pacemaker.
Increase. Typically will increase to maintain same cardiac output.
Bradycardia. A doctor's exam can tell you lots of things about your slow heart rate. People can have heart rate normally if they do regular exercises, if they are on certain medications that can cause slow heart rate. Also if they have sinus node dysfunction, as well as if they have complete heart block. Most importantly if they have vagus stimulation for any reason.
A few things... An experienced doctor can narrow down the diagnoses depending on how slow, regular, or irregular your heart rate is. Also, your medical history, medications, etc. Can lead to some conclusions. However, the best next test is an ekg to really examine the heart rhythm.
I have a slow heart rate, also extra beats, which they tell me are benign. Stress test ok, my thyroid is stable with meds. Why do I have these symptom?
Stress, Perhaps. Learn to relax deeply and let go of stress, and especially any anxiety or inner pressure (http://drmiller. Pinnaclecart. Com/balance-mind-and-emotions/abolish-anxiety-2-cds/28 is a valuable program). Sometimes the generalized irritability of the nervous system may have a role to play. If a week of sheer relaxation in a vacation place diminishes the extra beats, think stress. More at drmiler. Com.
Possibilities.... Include low serum potassium (from anti-bp or other rx), "escape" heart beats that occur when one's hr is unusually low from stress, rx, exercise fitness or underlying alternative electrical cardiac pathways. Not a bad idea to seek cardiology advice.