A technique for improving accuracy of the pulmonary artery diastolic pressure as an estimate of left ventricular end-diastolic pressure. Pulmonary artery diastolic pressure (PAD) is often used to estimate left ventricular end-diastolic pressure (LVEDP) when artifact, respiratory variation, or technical difficulties make the wedge pressure difficult to identify on the waveform. To determine which point on the PAD waveform best estimated LVEDP, we performed studies in 100 adults undergoing routine diagnostic cardiac catheterization. During normal spontaneous respiration, simultaneous recordings of the electrocardiogram, PAD, and LVEDP were obtained. Three end-expiratory measurements of PAD were recorded: at the lowest point on the waveform (PAD), at 0.04 seconds (PAD 0.04), and at 0.08 seconds (PAD 0.08) after the onset of the QRS complex. The PADs were correlated with LVEDP by linear regression. PAD 0.08 correlated best with LVEDP (r = 0.88, standard error of the estimate [SEE] = 3.6 mm Hg) whereas PAD 0.04 and PAD correlated slightly less strongly (r = 0.86, SEE = 4.0 mm Hg; r = 0.82, SEE = 4.4 mm Hg respectively). Therefore, when the wedge pressure is not easily determined, PAD 0.08 may be the best point on the waveform to use when attempting to estimate LVEDP in the clinical setting. 