> BACKGROUND: The accuracy of flow-related changes in aortic valve area (AVA) determined by the Gorlin formula or the continuity equation remains disputable. However, anatomic AVA can be determined by using by direct planimetry of transesophageal echocardiography (TEE). The purpose of this study was to assess the impact of changes in flow on AVA determined by TEE using direct planimetry. METHOD: Determination of AVA by TEE using direct planimetey was performed intraoperatively under three different hemodynamic conditions - pre-dobutamine (baseline) period, post-dobutamine period, post-CABG period - in 17 CABG patients and cardiac output (CO) with left ventricular ejection fraction (EF) were also determined by TEE simutaneously. The changes in aortic flow were induced by dobutamine infusion. RESULTS: AVA at pre-dobumaine period, post-dobutamine period, and post-CABG period were 2.99+/-0.80 cm2, 3.01+/-0.79 cm2, and 3.01+/-0.80 cm2, respectively. Before dobutamin infusion, CO and EF were 2.01+/-0.64 L/min and 47+/-10%. After dobutamine infusion, CO and EF were 3.03+/-1.05 L/min, 54+/-9% respectively and significantly increased by 54%, 18% than those measured before dobutamine infusion (p<0.01, p<0.01), respectively. After CABG, CO and EF were 3.86+/-1.86 L/min and 58+/-11% and also significantly increased by 98%, 26% than those measured before dobutamine infusion (p<0.01, p<0.01), respectively. However, despite of these significant hemodynamic changes, there were no significant changes in AVA and no significant correlations between these hemodynamic and AVA changes, neither at post-dobutamine period nor post-CABG period. CONCLUSION: The acute changes in CO and EF do not result in significant alterations in the anatomic AVA determined by TEE using direct planimetry. Thus, TEE using direct planimetry could be accurate and useful in the determination of AVA in hemodynamically unstable patient.