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The diastolic pressure difference (DPD) is recommended to differentiate between isolated postcapillary and combined pre-/postcapillary pulmonary hypertension (Cpc-PH) in left heart disease (PH-LHD). However, in usual practice, negative DPD values are commonly calculated, potentially related to the use of mean pulmonary artery wedge pressure (PAWP). We used the ECG to gate late-diastolic PAWP measurements. We examined the method’s impact on calculated DPD, PH-LHD subclassification, hemodynamic profiles, and mortality.We studied patients with advanced heart failure undergoing right heart catheterization to assess cardiac transplantation candidacy (N=141). Pressure tracings were analyzed offline over 8 to 10 beat intervals. Diastolic pulmonary artery pressure and mean PAWP were measured to calculate the DPD as per usual practice (diastolic pulmonary artery pressure–mean PAWP). Within the same intervals, PAWP was measured gated to the ECG QRS complex to calculate the QRS-gated DPD (diastolic pulmonary artery pressure–QRS-gated PAWP). Outcomes occurring within 1 year were collected retrospectively from chart review. Overall, 72 of 141 cases demonstrated PH-LHD. Within PH-LHD, the QRS-gated DPD yielded higher calculated DPD values (3 [−1 to 6] versus 0 [−4 to 3] mm Hg; P<0.01) and a greater proportion of Cpc-PH (24% versus 8%; P<0.01) versus the usual practice DPD. Cases reclassified as Cpc-PH based on QRS-gated DPD demonstrated higher pulmonary arterial pressures versus isolated postcapillary pulmonary hypertension (P<0.05). One-year mortality was similar between PH-LHD groups.The DPD calculated in usual practice is underestimated in PH-LHD, which may classify Cpc-PH patients as isolated postcapillary pulmonary hypertension. The QRS-gated DPD reclassifies a subset of PH-LHD patients from isolated postcapillary pulmonary hypertension to Cpc-PH, which is characterized by an adverse hemodynamic profile.