A subject's heart rate is determined. A heart rate monitor receives a Doppler signal reflected from an artery of a target, performs demodulation and heart beat recognition techniques to determine a set of features in each frame of the signal. Pattern classification is performed to determine if the extracted feature sequence is associated with heart beats. The pattern classification may include finding the optimal state sequence by calculating the probability of each allowable state sequence based on the extracted feature sequence and heart beat models or additional noise models. Or, a heart beat candidate is determined using frame energy and dynamic thresholding followed by computing the probabilities between the feature sequence and each stored heart beat model or additional noise models. Or, heart beat candidates are determined using frame energy and dynamic thresholding which compute the similarity between the feature sequences and each of the stored heart beat templates.
