Objective: Transmitral blood flow produces a vortex ring (quantified using vortex formation time [VFT]) that enhances the efficiency of left ventricular (LV) filling. VFT is attenuated in LV hypertrophy resulting from aortic valve stenosis (AS) versus normal LV geometry. Many patients with AS also have aortic insufficiency (AI). The authors tested the hypothesis that moderate Al falsely elevates VFT by partially inhibiting mitral leaflet opening in patients with AS. Design: Observational study. Setting: Veterans Affairs medical center. Participants: Patients with AS in the presence or absence of moderate Al (n = 8 per group) undergoing aortic valve replacement (AVR) were studied after institutional review board approval. Interventions: None. Measurements and Main Results: Under general anesthesia, peak early LV filling (E) and atrial systole (A) blood flow velocities and their corresponding velocity-time integrals were obtained using pulse-wave Doppler transesophageal echocardiography (TEE) to determine E/A and atrial filling fraction (beta). Mitral valve diameter (D) was calculated as the average of major and minor axis lengths obtained in the midesophageal bicommissural (transcommissural anterior lateral -posterior medial) and LV long-axis (anterior-posterior) TEE imaging planes, respectively. VFT was calculated as 4.(1-beta).SV/pi D-3, where SV = stroke volume measured using thermodilution. Hemodynamics, diastolic function, and VFT were determined during steady-state conditions before cardiopulmonary bypass. The severity of AS (mean and peak pressure gradients, peak transvalvular jet velocity, aortic valve area) and diastolic function (E/A, beta) were similar between groups. Moderate centrally directed Al was present in 8 patients with AS (ratio of regurgitant jet width to LV outflow tract diameter of 36 +/- 6%). Pulse pressure and mean pulmonary artery pressure were elevated in patients with versus without Al, but no other differences in hemodynamics were observed. Mitral valve minor and major axis lengths, diameter, and area were reduced in the presence versus the absence of Al. VFT was increased significantly (5.7 +/- 1.7 v3.2 +/- 0.6; p = 0.00108) in patients with AS and Al compared with AS alone. Conclusion: Moderate Al falsely elevates VFT in patients with severe AS undergoing AVR by partially inhibiting mitral valve opening. VFT may be an unreliable index of LV filling efficiency with competitive diastolic flow into the LV. Published by Elsevier Inc.