The present work is an attempt to provide a general overview on the current methods and applications of heart rate variability (HRV), starting from the underlying mechanisms of cardiac rhythmic automaticity and the influence on heart rate of biological modulators, namely autonomous nervous system. Different evaluation methods for HRV are compared in what concerns the duration of the records under analysis and the mathematical approach (spectral/non-spectral). Finally, clinical applications of HRV are mentioned, some of them the Department is particularly interested in, namely coronary heart disease, heart failure and diabetic neuropathy. The authors conclude, minding some aspects susceptible of discussion in the future of this technique.