Abstract: A method and apparatus for measuring activity of the autonomic nervous system of a patient involves obtaining ECG signals form the patient while the patient is at rest, measuring the R-R intervals for adjacent PQRS portions of the signals and generating a Poincare plot from the R-R intervals. The ECG signals are obtained for a period of less than one hour, and from the Poincare plot a determination can be made as to whether the autonomic activity represented by the plot can be used to quantify a degree of heart failure in the patient. The level of sympathetic activity of the patient can be quantified by determining a correlation dimension corresponding to the plot, and then a degree of heart failure in the patient determined on the basis of the correlation dimension when it lies outside a predetermined range. Furthermore, the level of parasympathetic activity for the patient can also be quantified by reference to the width of the plot about a line perpendicular to the line of identity of the plot.