The general nature of flow-disturbances and turbulence in fluid flows, and the special features which may govern their appearance in unsteady flows, are considered. A hot-film anemometer system, modified for use within arteries, has been used to examine flow disturbances in the aorta. Results suggested that the extent of flow-disturbances may be influenced by both peak flow velocity and pulse-rate, expressed in terms of the relevant fluid dynamic parameters. Possible underlying mechanisms are discussed, and power spectra for laminar and highly disturbed aortic velocity waveforms presented.