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 <1.0 cm² or indexed aortic valve area <0.6 cm²/m², mean gradient <40 mm Hg, indexed stroke volume <35 mL/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). No improvement 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.