Abstract: A microprocessor configured to receive and process digitized signals derived from an analogue ECG signal is provided. An example microprocessor comprises a beat detection unit configured to receive the in-phase and quadrature phase band power signals, calculate a band power value and an adaptive threshold value, and compare said band power value with said adaptive threshold value to detect a QRS complex of the ECG signal indicative of a detected valid beat; and an R peak detection unit configured to receive the digital ECG signal and information about the detected valid beat, select a portion of the received ECG signal as a first time window around the detected valid beat; determine the location of a first R peak position; and perform a time domain search in a second time window around said first R peak position in order to refine the location of an R peak position.