In this book, Heart rate from RR and PP interval series is compared for various MIT/BIH and fantasia database The heart rate is generally determined by detecting R peaks and calculating the RR intervals.This is because R peak has highest amplitude among various wave components of the ECG signal and therefore it is easier to detect the R peak locations. The heart cycle actually starts from P wave , so the PP interval series constitutes the actual heart rate time series. The P wave represents the spread of electrical activity over the atrium. In the detection algorithm for P-wave, firstly T-wave is detected in reference to R-peak. This method is efficient, simple to implement and can be easily modified to adapt to different ECG waves.The heart rate comparison with PP and RR intervals is done for various MIT/BIH and Fantasia database using the algorithm that starts from pre-processing of the raw ECG signal and ends with the heart rate calculation. It is concluded from comparison results that heart rate calculated from RR and PP interval time series individually is approximately same.