The reduction of heart rate variability also is regarded as a sensitive parameter of autonomic dysfunction, which contributes to the compromise of cardiac reserve in old age. Apart from typical morphological features and functional deterioration, e.g. diastolic dysfunction, the senescent heart is typically characterized by a narrowed heart rate variability. Efforts have been made to estimate the cardiac age of an individual by this compromised heart rate variability, which may be divergent to the biological age. In recent years diverse approaches were proposed to measure cardiac age on the basis of heart rate variability. The published mathematical formulae were mostly validated with small patient groups and have presently not entered clinical practice. Still heart rate variability is an accepted surrogate parameter of cardiac ageing and is amenable by therapeutic measures, e.g. beta-blockade.