An electronic stethoscope system comprising a device to capture an acoustic heart signal from a patient and a neural network to classify the data into heart sound categories to provide time series sound category data comprising, for each of a succession of time intervals, category probability data representing a probability of the acoustic signal falling into each of the categories. The stethoscope also includes one or more heart state models each having a sequence of heart cardiac cycle states, a system to fit the time series sound category data to the models and determine timing data for the sequence of heart states and a confidence value for the model fit, and an output to output one or both of a model fit indication dependent upon the confidence value and an indication of the timing data.