We read the report entitled “A Simple Echocardiographic Method to Estimate Pulmonary Vascular Resistance.” It showed the equation pulmonary artery systolic pressure/right ventricular outflow tract velocity time integral + 3 correlated best with pulmonary vascular resistance. We have previously shown that in patients with congenital heart disease, right ventricular pre-ejection period/velocity time integral <0.4 s/m correlated with pulmonary vascular resistance <3 Wood unit (WU) × m ² with 97% accuracy. Right ventricular pre-ejection period/velocity time integral between 0.4 and 0.6 s/m correlated with pulmonary vascular resistance WU × m ² between 3 and 7.5 with 91% accuracy. Values >6 s/m correlated with PVR >7.5 WU × m ² with 94% accuracy in children. Our formula is also simple to use, but it was not referenced in your report, so we are writing to inform you of it.