I was doing some cardio work this weekend and this question came to mind:
What is the lowest recorded resting heart rate for an otherwise healthy individual? I’m guessing it may be from a cross country skier or cyclist.
I believe that suspected drug cheat Lance Armstrong has recorded resting rates as low as 32 beats per minute - less than half the average healthy heart beat.
This site indicates that athletes routinely achieve 40s or even mid-30s, although numbers that low are considered “bradycardia” unless the diagnosing physician knows you are an endurance athlete who trains regularly. I have a resting heart rate of about 50 if I’ve been training.
One runner here clocks in a “freakish” time of 28bpm, talking about “lots of time at altitude.” This is the same number claimed by Bernard Hinault, French cyclist. Miguel Indurain claims 29bpm, which basically makes him legally dead. 
Lance Armstrong “only” claims 32-34. Wikipedia ignores these sources and cites 35 as the lowest heart rate of a Tour de France rider.
That’s interesting. I just now clocked mine at 25 in 30 seconds (50-52) and although I exercise regularly I am hardly a trained athlete.
Mid 50s aren’t all that surprising for someone who exercises regularly, and is in good cardio shape.
While my resting rate at (35 - 2 days) is about 64 I’m hardly “in shape” any more.
When I was running track in high school, and began giving blood, the nurse had to take my pulse 3 times to insure she had gotten it right. It was 51, and I certainly didn’t look like an athlete. I had, however, been on the distance running team for spring track, the cross country team, and had previously ridden my 10 speed bicycle nearly 100 miles a week, so my heart and lungs were in great shape! (If only I had kept it up…)
-Butler
When i was in the hospital having a surgery, i had a resting heart rate of 17. When i was resting in the hospital awake i had a resting heart rate of 44. At 200lbs 6ft im a pretty big guy. All the nurses thought i was on steroids but eventually came in and said “alright your healthy”. I had a cyst on my tailbone from when i was young i fell on it really hard off a bike.
Of course, the average resting heart rate of a zombie is zero.
That said, I had a friend who was a competitive cyclist. She told me that she wore her pulse rate monitor to bed once, and it woke her up when her pulse rate fell under 30 BPM, and it tripped the alarm…
I am not an athlete. When my resting heart rate fell to the mid 30s, I got a pacemaker. Well, there was more to it than that. They put a 24 hour cardiogram on me and discovered that during the night, I went as many as 7 seconds with no beat.
I reached a milestone this year that my rest heart rate is now a lower number than my age.
I’m only 26 tho 
no pacemaker for me yet! I deadlifted 405 lbs the other day too.
A long time ago, my resting heart rate was in the low 40s. I was in very good shape then.
My daughter’s was in the upper 30s when she was in her teens-early twenties. She raced bicycles and won a couple of 24 hour races doing over 355 miles in one.
Sometimes it is just the way someone is built. My range has been upper 50s when not exercising to low 40s when I am sticking with whatever my program is of the season. My personal goal is to reach the point that my resting heart rate is half my age. 
My eldest son runs the same and is not particularly compliant with a fitness program. So both genetics and fitness contribute in any particular person.
For historical context I offer up this article from 1972 looking a some asymptomatic elderly individuals with bradycardia, down to 40. The concern was that bradycardia could cause cerebral dysfunction. The answer? Nah. They just get more out with each beat (higher stroke volume). By the 90s bradycardia, even if not due to fitness, was being thoughta good thing.
IN any case, to answer the op itself, there is the claim ofthis New England Journal of Medicine review from 2000.
So down to 30 anyway.