Heart Rate Records
Human heart rate can range from 20-30 at rest, to over 200 during maximum exercise (and also disease). Extremes of heart rate are also possible with certain medical conditions (see Heart Rate FAQ). This discussion is about heart rate extremes (maximum and minimum) in healthy individuals.
Resting Heart Rate
The average resting heart rate is around 70 beats per minute, with athletes having a lower level due to an enlarged and more efficient heart from training adaptation. (see the Resting Heart Rate Chart).
According to the current listing for the Guinness World Records (and also in the printed books since 2009), the lowest resting heart rate on record is 27 bpm (beats per minute) belonging to Martin Brady (b. 24 March 1969 in the UK) - tested at the Guernsey Chest and Heart Unit, Channel Islands, UK on 11 August 2005.
At the time of the 2004 printed edition Guinness World Records (Guinness Book of Records), the lowest heart rate on record was 28 bpm as recorded by Spanish cyclist and five time Tour de France winner Miguel Indurain, who was tested at the University of Navarra, Pamplona, Spain, in 1995.
There are other (unconfirmed) reports of Lance Armstrong having a low resting heart rate. According to his official website, he has a resting heart rate of 32-34 bpm (with a maximum heart rate of 201 bpm).
Maximum Heart Rate
We have no records of maximum heart rate. A rough estimation of someone's maximum heart rate is using the commonly used formula of 220 minus your age in years (220-age). This implies that as you get older, your maximum heart rate decreases. It is not uncommon to see maximum heart rates well over 200 during maximal exercise tests. Peak levels may be achieved transiently. For records sake, a heart rate should be at a peak level for a set time, maybe 10-15 seconds. Resting heart rate levels are measured at 'steady state', often averaged over a one minute period.
If you want to test your maximum heart rate, it is best measured during a maximal exercise test, in which the body is pushed to its limit. In this case, you must ensure you are medically fit and used to pushing yourself to the limit as it can put excessive demand on the heart.