Resting heart rate and fitness

A lot of it is genetics. My RHR has always been on the low side even when I was a lot less fit. When I was a teen it was bordering on too low. My friend, on the other hand. Has always been very active. She goes to the gym 6 days a week and has run marathons. However, her RHR and blood pressure have always been high and she needs to take blood pressure medication and can't be on hormonal contraception because of it. Sometimes its just the luck of the draw.