Indices of Doppler-derived velocity waveforms of arteries perfusing the brain are used as relative measures of neonatal brain blood flow. Using a dog model, we investigated the influence of changes in myocardial contractility, induced by dobutamine, on the blood flow velocity waveform of the vertebral artery. The following indices of the velocity waveform were investigated during control states and during 5 or 10 micrograms/kg/min dobutamine infusion: peak systolic flow velocity (PSFV), temporal mean flow velocity (TMFV), end-diastolic flow velocity (EDFV) and acceleration time (ACC-time). PSFV and ACC-time of the vertebral artery showed a strong relationship with myocardial contractile state. These results indicate that PSFV of an artery supplying the brain or indices which combine PSFV with MFV or EDFV should not be used for noninvasive assessment of brain blood flow or cerebral vascular resistance. ACC-time may prove to be very useful in assessing changes in myocardial contractile state.