We agree with Dr Giardini that alternative explanations, including some of those he cites, may exist to further explain Doppler-cardiac catheterization PASP discrepancies in patients with pulmonary hypertension. We were particularly interested in the possibility that viscous factors may have accounted for some of the inaccuracies we observed in our study. We, thus, created a multivariate model from our simultaneous Doppler-cardiac catheterization data to evaluate whether oxygen saturation and/or hemoglobin levels were associated with differences in Doppler-cardiac catheterization estimates of PASP. Neither oxygen saturation nor hemoglobin level were associated with differences in Doppler-cardiac catheterization estimates of PASP (β coefficient, − 1.72 ± 1.95 and − 2.24 ± 3.83, respectively; P = not significant). Insufficient sample size (N = 21) is a possible explanation for these negative results. Regarding the impact of inertial forces, most patients with severe pulmonary hypertension tend to have right atrial enlargement, which may minimize the impact of inertial forces and pressure recovery. Other explanations for the discrepancies may also exist beyond those cited in our study or by Dr Giardini, including the impact of changes in intrathoracic pressure occurring with respiration, which are not routinely accounted for during the standard noninvasive Doppler examination but are easily accounted for by measuring PASP at end-expiration during invasive cardiac catheterization.