Your heart pumps continually until you die -- and this cessation may actually be the reason that you do die. The average heart pumps over 2 billion times for an average lifespan. It manages over 100,000 beats per day. This is a very important organ by any measure: It is the engine of your body.
Range of Heart Rates
The human heart has a very flexible pumping range. The healthy range can be from 30 to 220 beats per minute (BPM). An elite athlete, like Lance Armstrong, can have a resting heart rate in the 30s and a maximum rate (when young) of over 200 beats per minute. Diseased hearts can also pump very high or very low.
Normal, resting heart rates vary according to genetics, fitness, stress and other factors. The healthy range, excluding some athletes and very fit people, is often given as between 60 to 90 beats per minute. Even slightly lower or higher may be normal. Children tend to have higher heart rates than adults.
In fit recreational athletes, the range can be 45 to 55 beats per minute. In elite endurance athletes, below 50 and sometimes below 40 beats per minute is the norm. The famous multiple Tour de France winner, Miguel Indurain, was rumored to have a resting heart rate of 28! On the other hand, the brilliant US middle distance runner and one-time world record holder for the mile, Jim Ryun, reputedly had a resting heart rate of around 70 BPM. Heart rate is variable for individuals but norms do exist for most people.
The Athletic Heart
The heart has four chambers and the appropriate valves for controlling blood flow to and from the lungs for respiration, and to the rest of the body for blood supply to tissue and organs. The largest chamber is the left ventricle, which pumps blood through the aorta (artery) for general circulation. The typical volume of blood pumped at rest and normal activity is around 5 liters/minute, with volumes increasing to 25 to 45 liters/minute during intense activity -- the highest being for elite athletes.
With training, athletes -- even recreational athletes -- can get heart enlargement called "athlete's heart." The type of change to the left ventricle chamber depends on the type of training you do. Endurance training (marathoners, cyclists, triathletes) tends to increase the internal diameter of the chamber, whereas strength training (lifters, bodybuilders, wrestlers) tends to increase the wall thickness of the chamber. Interestingly, crossover trainers that do both endurance and weight training tend to have the largest internal diameter and the largest ventricle mass. Perhaps some synergy occurs with cross training.
The Diseased Heart
Compared to the athlete's heart, a diseased heart can also be enlarged, except the functional differences are substantial. A diseased heart has substantially less pumping power and efficiency. At low beats per minute, barely enough blood and oxygen gets through. The diseased heart has to beat faster to achieve the same blood and oxygen exchange as a healthy heart would at low BPM.
Abnormally high and irregular heart beats, called "atrial fibrillation", can be dangerous. Athletes may have occasional premature beats (perceived as single "skipped beats") but no more than the general population. Periods of truly irregular heart beats should always be evaluated by a physician.
Taking Your Pulse
You can measure your heart rate via the pulse at the radial artery of the wrist, or at the carotid artery of the neck. Use your middle and/or index fingers and not the thumb. The radial point is on the inside of the wrist near the wrist joint on the thumb side. The carotid is in the neck on either side, and easily found. Don't press too hard. Only take your carotid pulse one side at a time. Measure for 30 seconds and multiply by two to get your beats per minute. You could also use a heart rate monitor device.
Estimating Maximum Heart Rate
You may need to estimate or establish your maximum heart rate in order calculate training intensity, or to ensure you do not exceed a certain threshold when recovering from heart surgery or managing heart disease or a similar chronic condition. If you are on heart or blood pressure drugs, this can get complicated, so it's best to get advice or measurement from your doctor or an experienced exercise physiologist. Training intensity ranges include from 50 to 75% of maximum heart rate, but experienced athletes train at higher intensities.
You can use the standard estimate calculation of 200 minus your age to give a rough estimate. For example, at age 40, maximum heart rate could be around 180. Various other formulas are available for men, women, and trained athletes. For direct measurement, the best way is to do a medically supervised maximum stress test on a treadmill. Personal electronic heart rate monitors are also useful. You should sustain a maximum effort for 10 to 20 seconds to record a maximum heart rate. Don't do this unless you are used to exercising and have no other medical conditions that would make this dangerous. Ask you doctor if in doubt.
In conclusion, it's worth knowing how the heart works and is affected by exercise and physical activity, but for most casual and recreational exercisers, measuring heart rates and training ranges may not be necessary.
Pluim BM, Zwinderman AH, van der Laarse A, van der Wall EE. The athlete's heart. A meta-analysis of cardiac structure and function. Circulation. 2000 Jan 25;101(3):336-44.