A method and apparatus to detect irregular heart activity and estimate heart rate. In one embodiment, the heart rate estimation apparatus includes a group of six RR storage structures that receives an input of six successive RR interval values. The apparatus also includes a probability engine coupled to the group of RR storage structures, the probability engine is operable to calculate and output a mean value of the six RR interval values and a median value of the mean value and the six RR interval. In one embodiment, the apparatus carries out a method including the acts of determining a plurality of interval values between successive R waves; determining a mean of a group of six interval values; determining a median interval value for a group including the group of six interval values and the mean of the group of six interval values; and determining a running average of interval values between successive R waves using the median interval value.