Heart rate variability (HRV) is a noninvasive, practical and reproducible measure of autonomic nervous system function. Although the heart is reasonably stable, the time between two beats (R-R) can be very different. HRV is the time variation between two consecutive heartbeats. HRV is believed to correspond to the balance between the sympathic and parasympathic influences on the intrinsic rhythm of the sinoatrial node. HRV is influenced by lifestyle factors, including physical activity, eating habits, sleep pattern, and smoking. In adults, decreased HRV is associated with a higher risk of cardiac events, including death, and is a predictor of hypertension. HRV may also have predictive value for life expectancy and health. HRV changes due to lifestyle factors precede the onset of cardiovascular disorders. Measurement of HRV and its components is of major interest for medical practitioners and public health specialists, in order to predict and evaluate the risk of cardiometabolic events related to lifestyle factors.