Tc-99m MIBI is used for myocardial imaging and first-pass studies. However, little is known about its utility in the assessment of left ventricular diastolic function. The authors retrospectively compared first pass studies of Tc-99m MIBI at rest with Doppler flow velocity measurements to assess left ventricular diastolic performance. Thirty-nine patients who had both studies performed within 48 hours of each other were evaluated. Three indices of diastolic function were measured by first pass Tc-99m MIBI ventriculography and Doppler echocardiography: 1) Time to peak early diastolic velocity; 2) normalized peak filling rate; and 3) half filling fraction. The results demonstrated a correlation of 0.82 (P < 0.001), 0.82 (P < 0.001), and 0.53 (P = 0.001) for the above indices, respectively. This study indicates that the indices of left ventricular diastolic function by first pass Tc-99m MIBI compare favorably with those derived from Doppler flow velocity measurements in which the diagnostic value has been previously established. Both methods accurately reflect diastolic flow and may facilitate clinical evaluation of diastolic function.