Heart rate
The heart rate is the number of contractions of the heart in one minute. The adult human heart beats at about 70 beats per minute, but this varies between people.
The body can increase the heart rate in response to a wide variety of conditions in order to increase the cardiac output (the amount of blood ejected by the heart per unit time).
The pulse is the most straightforward way of measuring the heart rate, but it can be deceptive when some strokes do not lead to much cardiac output. In these cases (as happens in some arrhythmias), the heart rate can be (much) higher than the pulse.
Control of heart rate
The heart contains cardiac pacemakers that spontaneously cause the heart to beat. These can be controlled by the autonomic nervous system and circulating adrenaline. The heart beats more quickly than average in an obese person, and less quickly than average in athletes.
Tachycardia
A tachycardia is a heart rate more than 100 beats per minute.
Bradycardia
Bradycardia is defined as a heart rate less than 60 beats per minute. Some consider a rate less than 50 beats per minute to define a bradycardia.
Trained athletes tend to have slow resting heart rates, and resting bradycardia in athletes should not be considered abnormal if the individual has no symptoms associated with the bradycardia.
The term relative bradycardia is used to explain a heart rate that, while not technically below 60 beats per minute, is considered too slow for the individual's current medical condition.
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