A method and apparatus to detect irregular heart activity based upon a ventricular activity analysis, P wave activity, similarities in R wave to R wave intervals, and a state evaluation. The invention includes a beat classification module that receives ECG information as an input. The beat classification module determines whether the heart beat being analyzed falls within classifications that are suitable for use in analyzing whether an irregular condition exists. If the beat falls within a class suitable for analysis, the ECG information is fed to an interval calculator. The interval calculator determines the interval between successive R waves. The information from the interval calculator is provided to a probability engine and to a contextual analysis module. The probability engine is designed to detect atrial fibrillation based upon beat classification and RR interval values from the interval calculator. The probability engine outputs a state variable that indicates a probability of whether an irregular condition is present. The contextual analysis module matches predefined maps to a running map of the current ECG information. The contextual analysis module also determines the similarity between consecutive RR intervals and checks for sequences of matching classes. ECG information is also supplied to a P wave detection module to detect the presence of P waves. Information from the probability analysis engine, the contextual analysis module, and the P wave detection module is then provided to a state evaluation module. The state evaluation module uses the outputs of the three modules to determine whether an irregular condition exists.