The purpose of this study was to compare the aortic valve effective orifice area (EOA) estimated between Doppler echocardiography and 4D flow MRI using a consecutive same-day study design to minimize inter-modality variability. Peak velocity and left ventricular outflow tract area were higher for MRI but velocity time integral was higher for echo. These differences were compensatory when computing EOA, which resulted in good agreement despite discrepancies in echo vs MRI. Volumetric 3D velocity information has the potential to better estimate EOA in the presence of eccentric jets. This potential strength will be studied in aortic stenosis patients.