Abstract: The heart rhythm is directly related to the electrical activity of the heart. Electrocardiogram (ECG) is generally used for obtaining information about the heart rhythm. In this paper, a method for calculating heart rhythm variation using the Phonocardiogram (PCG) and a method for finding characteristics of the that signal is described. The average heart rate is calculated from the Shannon energy signal and characteristics are found using mean, variance and autocorrelation. The analysis window for calculating the instantaneous heart rate is repeated for entire signal for every one second shift. It is shown that even for normal persons there is significant variation in the heart rate. Heart rate variation shows bi-modal distribution for an abnormal case.