Background: Echocardiographic evaluation after transcatheter aortic valve implantation (TAVI) includes estimation of effective orifice area (EOA). EOA calculation depends on sub-valvular stroke volume (SV), which depends on sub-valvular diameter and velocity time integral (VTI). The Medtronic CoreValve area changes throughout its length. We aimed to (i) compare SV at two sites of flow acceleration: ‘pre-stent’ and ‘in-stent, pre-valve’, (ii) assess effects of possible differences in sub-valvular SV on EOA, and (iii) assess agreement of measurement of EOA calculation after CoreValve TAVI. Methods: We studied 43 patients after CoreValve implantation. All had transthoracic echocardiography 5-7 days after TAVI. Sub-valvular SV was measured ‘pre-stent’ and ‘in-stent, pre-valve’. Measurement agreement was assessed by root mean square (RMS) differences and Bland-Altman analyses. Results: SV was consistently higher ‘in-stent, pre-valve’ compared with ‘pre-stent’ (62±20ml vs. 53±19ml, p<0.001), so that EOA was correspondingly larger using ‘in-stent, pre-valve’ measurements (1.7±0.5cm2 vs. 1.4±0.5cm2, p<0.001). Between-observer RMS difference for calculation of EOA was higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.53 cm2 vs. 0.23cm2, difference from zero 0.17, p=0.002). Though sub-valvular diameter measurements were variable, VTI variability was additionally higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.42cm vs. 0.6cm, difference from zero -1.74, p=0.11). Conclusion: Calculation of EOA after CoreValve TAVI is highly dependent on sub-valvular sample position. EOA may be underestimated using ‘pre-stent’ SV, and overestimated using ‘in-stent, pre-valve’ SV. Limitations in SV reproducibility suggests EOA should be used in conjunction with other indices of valve function in serial assessment of CoreValve function following TAVI.