We correlated the new diastolic index 'delay of apical peak velocity', as measured by colour M-mode Doppler, with radionuclide ventriculographic indices of ventricular function. Thirty-seven patients with coronary artery disease participated in the prospective and blinded study, which included repeated acquisitions to determine the effect of realigning the Doppler sample beam. In multiple regression, neither peak filling rate, left ventricular phase histogram width nor ejection fraction were statistically significantly related to delay of apical peak velocity. The standard deviation of the differences between duplicate colour M-mode acquisitions corresponded to half the reference range of the index. We conclude that in this blinded investigation, the new Doppler index did not provide information about ventricular function equivalent to radionuclide ventriculography. The index may be significantly influenced by sample beam position.