It was recently shown that invasively determined right ventricular (RV) stiffness was more closely related to the prognosis of patients with pulmonary hypertension than RV systolic function. So far, a completely noninvasive method to access RV stiffness has not been reported. We aimed to clarify the clinical usefulness of our new echocardiographic index of RV operating stiffness using atrial-systolic descent of the pulmonary artery-RV pressure gradient derived from pulmonary regurgitant velocity (PRPGD_AC) and tricuspid annular plane movement during atrial contraction (TAPM_AC). We studied 81 consecutive patients with various cardiac diseases who underwent echocardiography and cardiac catheterization. We measured PRPGD_AC and TAPM_AC using continuous-wave Doppler and M-mode echocardiography, respectively, and calculated PRPGD_AC/TAPM_AC. RV end-diastolic pressure (RVEDP) and RV pressure increase during atrial contraction (ΔRVP_AC) were invasively measured, and RV volume change during atrial contraction (ΔV_AC) was calculated from echocardiographic late-diastolic transtricuspid flow time-velocity integral and tricuspid annular area; thus ΔRVP_AC/ΔV_AC was used as the standard index for RV operating stiffness. PRPGD_AC/TAPM_AC well correlated with ΔRVP_AC/ΔV_AC (r = 0.84, p < 0.001) and RVEDP (r = 0.80, p < 0.001), and the area under the receiver operating characteristic curve to discriminate RVEDP > 12 mmHg was 0.94. Multivariate regression analysis revealed that PRPGD_AC/TAPM_AC was the single independent determinant of ΔRVP_AC/ΔV_AC (β = 0.86, p < 0.001). PRPGD_AC/TAPM_AC is useful to estimate RV operating stiffness and a good practical indicator of RVEDP.