Objectives: To describe a method for the estimation of transaortic flow from multidetector computer tomography (MDCT). Background: Cardiac MDCT may not allow instantaneous flow measurement yet the components of flow, namely, volume change over time and lumenal area are recorded. Methods: In 36 patients, the transaortic flow velocity was determined on transthoracic echocardiography and also with cardiac MDCT as follows: On MDCT an axial orientation through the aortic root was obtained so that the nadir of all three aortic leaflets could be seen simultaneously in one axial image. Aortic valve area (AVA) was determined by planimetry and left ventricular volumes by endocardial border mapping at every 5% increment of the RR intervals. Flow velocity was then calculated as the incremental ejection volume Ã· duration of the increment Ã· AVA. Results: The transthoracic echocardiography (TTE) peak velocity and MDCT peak velocity were highly correlated (r = 0.75, P < 0.01). Transaortic peak velocity was higher when measured by MDCT as compared to TTE, with respectively a median [IQ-range] of 4.5 [2.9-5.3] and 4.0 [3.0-4.6], P < 0.01. For the diagnosis of severe aortic stenosis greater concordance with TTE peak velocity was seen with MDCT peak velocity (sensitivity 100%, specificity 76%) than with MDCT AVA (sensitivity 74%, specificity 76%). Conclusions: We show for the first time that transaortic flow velocity can be estimated by dual-source MDCT and has a better sensitivity for the detection of severe aortic stenosis than AVA planimetry when compared to the gold standard of TTE peak flow velocity.