Heart rate variability is the marker of the heart\'s response to the autonomic nervous system activity. The decrease in HRV is a clinical predictive factor of overall cardiac mortality, and especially that of arrhythmia complications in the population after infarction. The parameters most significantly used in practice include SDNN and HRV index. Twenty-four-hour measurements are of higher predictive value, and an increase in the positive predictive value can be accomplished by multifactorial stratification. HRV is most frequently combined with ejection fraction and baroreflex sensitivity. The possibilities of HRV assessment are interesting also in coincidence with heart failure, arterial hypertension and atrial fibrillation also after heart transplantation. (Tab. 2, Ref. 63.).