Gap filling is provided in spectral Doppler ultrasound. Due to the cyclical nature of the cardiac system, data likely to be similar to data that would have been acquired without interleaving is copied into the gap generated by interleaving. Acquired data associated with the gap, such as adjacent to the gap, is correlated with other acquired data. By identifying similar data, acquired data temporally related to the similar data as the gap associated data is temporally related to the gap is found. This found data is likely to be similar to data that would have been acquired during the gap. The gap is filled with a copy of this data.