BACKGROUND: The projected aortic valve area (AVA) at a normal transvalvular flow rate using dobutamine is helpful to determine the actual severity of aortic stenosis (AS) and to predict risk of adverse events in low-gradient AS cases with unclear surgical indication. Our study aimed to identify the independent and incremental value of preload stress echocardiography-derived AVA to predict outcomes in patients with preserved ejection fraction and low-gradient AS. METHODS AND RESULTS: We prospectively performed echocardiographic studies in 79 patients with low-gradient AS (age, 77±7 years; 30% men) with preload stress echocardiography using leg positive pressure. AVA was calculated using AVA and transvalvular flow rate at baseline and during leg positive pressure. The primary end point was the decision for aortic valve surgery or cardiac death. During a median period of 19 months, 23 patients had the decision for aortic valve surgery, and none died during follow-up. In a stepwise multivariable analysis, indexed AVA (AVAi; hazard ratio, 2.00 per 0.1 cm/m decrease; 95% confidence interval, 1.36-2.96; <0.001) was associated with the primary end point. Using a receiver operating characteristic curve analysis, the best cutoff value of AVAi for predicting cardiac events was <0.72 cm/m. By incorporating AVAi into AVAi at baseline, continuous net reclassification index for cardiac events was 0.48 (=0.04). CONCLUSIONS: In patients with low-gradient AS, indexed AVA derived from preload stress echocardiography can be useful to predict risk of adverse events. The present article should be considered as a proof of concept study, and we think that larger multicenter studies are warranted.