LV elastance (Elv) denotes the slope of a line connecting a series of end-systolic pressure-volume relations during a load intervention. Non-invasive estimation is often done as LVESP/LVESV (simplified method, SM; smElv) which assumes that (A) intra-LV systolic blood pressure (smSBP) = 0.9 × brachial BP and (B) the Elv line intersects the volume axis (V₀) at zero. A more robust method exists which does not make assumption B (gold standard (GS) Elv: gsElv) but requires complex computation. We evaluated SM against GS in 22 consecutive patients (7 with heart failure, 32%; mean LVEF 43 ± 19%) attending our laboratory for echocardiography. Central pressure waveforms were obtained (radial artery tonometry; SphygmoCor, AtCor Medical, Sydney, Australia) and GS intra-LV SBP (gsSBP) was computed (aortic SBP + trans-aortic gradient; continuous-wave Doppler). gsElv was calculated as described previously.¹ smSBP and smElv were calculated as above. We found that intra-LV SBP was underestimated by SM (smSBP 117 ± 17 vs. gsSBP 126 ± 20 mmHg; p=0.002). The mean between-method difference was −8.4 ± 6.7 mmHg, range +6.5 to −17 mmHg). Nonetheless, SM overestimated Elv (smElv 3.4 ± 0.5 vs. gsElv 1.9 ± 0.8 mmHg/mL; p<0.001. The mean between-method difference (1.5 ± 0.7 mmHg/mL; range 0.6 to 2.7 mmHg/mL) was larger the more V₀ differed from zero (0.06 ± 0.03 mmHg/mL per 10 mL change in V₀; r=0.71, p<0.01). In conclusion, Elv obtained by SM differs markedly vs. GS, as a result of assumptions A and B.