so I was at the doctor’s office this morning for some routine stuff and I had a pulse of 42 (and that was while sipping on some Starbucks coffee ;))
The nurse took the measure twice and then the doctor said he had to examine me because of the low pulse. I told him I was training for triathlons and all and it was ok. But made me feel kind of good that I seem to be doing something right with the training…(I assume that is it?)
so is the pulse the same as the heart rate (forgive my ignorance, I guess I should know this - what is the difference if any?) and is 42 very low? I read anything under 70bpm is low and considered “bradycardia”?
High 30’s low 40s is pretty common among fit healthy athletes. Some actually have it dip down into the high 20s.
I’ve commonly had a pulse around 39-41 sitting during a visit to the doc and he has never seemed worried being he knows I work out 15+ hours a week. However on a overweight unfit person a pulse in that range can be considered dangerously bradicardic indicating possible heart issues.
I’m not a doctor, but 42 sounds normal for an athlete, especially an endurance athlete. My understanding is that HR is the times your heart beats and pulse is the measure of the surge of blood produced by your heart beating. You can have a HR but not have a pulse in some areas. For example, if your blood pressure is very low you may have a heartrate but only be able to detect a pulse on your neck (no pulse at your wrist or feet). Bradycardia means slow HR but is usually defined in terms of what is normal for the patient. A pulse or HR of 42 is lower than what is considered normal for vital signs but when I check someone’s pulse in the field and find something like 42 I consider the patient before becoming too concerned. For example, an obese smoker with a HR of 42 will concern me much more than a marathon runner with that pulse. So yeah, you’re bit brady, but I think you’ll live… 
It seems that most triathletes have unusually low resting hear rates. I’m new to triathlon, but I used to do a lot of biking and have always had a resting heart rate in the low 40’s.
A couple of years ago, I took out a life insurance policy on myself. As part of the application process the company sent me to someone (not a doctor) whose job was to give people physicals. He took my pulse three times and said he’d rarely seen someone with such a low resting heart rate. Told he he’d tested ex-Navy seals who didn’t have as low a rate. Made me feel pretty good. 
put your hrm on in the morning and lay there for a while totally still and see how low you can get it…my best was a 29 in college with a witness. nothing like starting your day with a p.r. for your heart rate