Analysis of heart rate variability (HRV) permits an assessment of sympathetic and parasympathetic activity from EKG recordings. Analysis of HRV may be performed in both the time and frequency domain by the application of mathematical principles of signal processing. HRV demonstrates abnormalities in myocardial infarction, sudden death, heart failure, autonomic neuropathy and hypertension. The technique is useful for assessing prognosis and for evaluating therapeutic interventions.