Heart Rate is the number of cardiac contractions occurring in a specified period, conventionally expressed as beats per minute (bpm). It reflects the frequency at which the heart is beating rather than the amount of blood pumped with each beat. In a resting adult, a commonly encountered resting range is approximately 60–100 bpm, although healthy individuals can have values outside this range, particularly trained athletes, whose resting rates may be considerably lower. Heart rate is regulated continuously to match cardiac output to the body's metabolic requirements. It therefore changes with physical activity, posture, temperature, emotional state, illness, medications, hydration and numerous other physiological influences.
The heart's rate is controlled principally by the autonomic nervous system and intrinsic electrical conduction system. The sinoatrial node normally initiates electrical impulses, which propagate through the atria and then through the atrioventricular node and ventricular conduction system. Sympathetic stimulation generally increases heart rate, while parasympathetic, particularly vagal, activity generally decreases it. Circulating hormones such as adrenaline can also increase cardiac rate. The relationship between heart rate and cardiac output is important because cardiac output is approximately the product of heart rate and stroke volume. Consequently, an increased heart rate does not necessarily mean that cardiac output has increased proportionally, particularly when very rapid rates reduce ventricular filling time.
Heart rate varies substantially according to circumstances. Exercise increases oxygen and nutrient delivery requirements and normally produces a predictable rise in heart rate, while recovery after exercise provides information about autonomic regulation and physical conditioning. Fever can raise heart rate, whereas some medications, endocrine disorders and disturbances of autonomic function can alter it in different directions. Anxiety, pain, caffeine, nicotine and dehydration may transiently increase the rate. Sleep generally reduces heart rate compared with waking activity. Age also influences normal values, with children normally having higher resting heart rates than adults and newborns having particularly rapid rates.
Heart rate can be measured manually by palpating a pulse, commonly at the radial artery, or electronically using electrocardiography, pulse oximetry, wearable devices and other monitoring technologies. The pulse rate is often a practical approximation of heart rate, but the two are not invariably identical. In some arrhythmias, not every cardiac contraction generates a palpable peripheral pulse of sufficient strength to be detected, producing a pulse deficit. Electrocardiography provides more detailed information because it records electrical activity and allows identification of rhythm and conduction abnormalities. Consumer wearable devices can be useful for trends but may be less reliable during movement, irregular rhythms or poor sensor contact.
Resting heart rate is clinically different from heart rate during exertion. A resting measurement should ideally be taken after an adequate period of quiet rest because recent exercise, emotional stress, stimulants or illness can produce temporary elevations. Repeated measurements can be more informative than a single isolated reading when assessing an individual's usual baseline. An unexpectedly high or low rate becomes more clinically meaningful when accompanied by symptoms such as chest discomfort, fainting, severe breathlessness, dizziness or marked weakness. The numerical value must therefore be interpreted alongside rhythm, symptoms, age, medications, medical history and the circumstances in which the measurement was obtained.
Tachycardia generally refers to an abnormally fast heart rate, while bradycardia generally refers to an abnormally slow heart rate, although precise thresholds and clinical significance vary according to context. Sinus tachycardia can be an appropriate physiological response to exercise, fever, pain or stress and is therefore not synonymous with a dangerous arrhythmia. Conversely, bradycardia can occur normally during sleep or in well-trained athletes but may also result from conduction-system disease or medications. Arrhythmia is a broader term referring to abnormal cardiac rhythm and may involve an abnormal rate, irregularity or abnormal origin of electrical activity. Distinguishing sinus rate changes from pathological rhythms usually requires clinical assessment and sometimes ECG monitoring.
Heart rate is used in many areas of healthcare and performance monitoring. Clinicians may follow it as part of vital-sign assessment, evaluate trends during acute illness, monitor response to treatment and use it alongside other findings when assessing cardiovascular status. In exercise science, heart-rate measurements can help describe training intensity and recovery, although individual variation means that generic percentage-based zones are not universally precise. Medications such as beta blockers deliberately reduce heart rate in some circumstances, making heart-rate-based exercise calculations less straightforward. The usefulness of the measurement therefore depends on understanding what physiological or clinical question it is intended to answer.
Heart rate has important limitations as a standalone indicator of health. A normal rate does not exclude cardiovascular or other disease, and an abnormal rate does not automatically establish a diagnosis. Stroke volume, blood pressure, oxygen delivery, cardiac rhythm and tissue perfusion all provide additional information. Some serious conditions can occur with a normal heart rate, while temporary physiological changes can produce values outside conventional reference ranges in healthy people.
The most useful interpretation considers the measurement's timing, method, trend, symptoms and clinical context. In acute care, a changing heart rate can be an important signal of physiological stress, but it should be interpreted alongside the complete clinical picture rather than treated as an isolated diagnostic test.
