Studies in paradoxical low-flow low-gradient aortic stenosis (PLFAS) have demonstrated conflicting outcomes with variable survival advantage from aortic valve replacement (AVR). PLFAS is a heterogeneous composition of patients with uncertainty regarding true stenosis severity that continues to confound decision-making for AVR. The purpose of this study was to investigate the utility of the Doppler acceleration (AT) to ejection (ET) time ratio (AT:ET) for prediction of prognosis and benefit from AVR in undifferentiated PLFAS. Patients with echocardiographic findings of PLFAS (aortic valve area<1.0cm2 or indexed aortic valve area<0.6cm2/m2, mean gradient<40mmHg, indexed stroke volume<35mL/m2, and left ventricular ejection fraction≥50%) were identified and grouped according to an AT:ET cutoff of 0.35. The primary outcome was a 5-year composite of cardiac mortality or AVR. Secondary outcomes included the individual components of the primary endpoint and all-cause mortality at 5 years. Effect of AVR was analyzed in the AT:ET<0.35 and≥0.35 groups. A total of 171 PLFAS patients (median age 77.0 years, 57% women) were followed for a median of 8.9 years. AT:ET≥0.35 was an independent predictor of the primary outcome (HR: 4.77 [95%CI: 2.94-7.75]; P< 0.001) with incremental value over standard indices of stenosis severity (net reclassification improvement: 0.57 [95%CI: 0.14-0.84]). AT:ET≥0.35 also remained predictive of increased cardiac death (HR: 2.91 [95%CI: 1.47-5.76]; P = 0.002) and AVR (HR: 8.45 [95%CI: 4.16-17.1]; P< 0.001), respectively, following competing risk analysis. No difference in all-cause mortality was observed. AVR in the AT:ET≥0.35 group was associated with significant reductions in 5-year cardiac (HR:0.09 [95%CI: 0.02-0.36]; P< 0.001) and all-cause mortality (HR: 0.16 [95%CI: 0.07-0.38]; P< 0.001). Noimprovement in survival from AVR was demonstrated in AT:ET<0.35 patients. AT:ET≥0.35 in PLFAS predicts poorer outcomes and/or need for AVR. In undifferentiated PLFAS patients, AT:ET may have a potential role in improving patient selection for prognostic AVR.