Nige,   Interesting question.  Your resting heart rate of 38 is definitely below what is considered normal (60-100).  However, physical fitness can definitely affect this.  I have seen professional basketball players who routinely have resting rates in the 30's. The question to be answered: is this low rate OK for you?    You will need to consult with your physician who will take a history and examine you.  He will then decide if further evaluation is necessary.  By your letter, your heart rate does respond to exercise as expected.  The need for a stress test will be determined by your physician.  Your father's history is also a factor in his decision process.   Thanks again,   Martin Cane, M.D.