We investigated whether the isovolumic relaxation time (IRT) and an interval from the start of opening to the maximal amplitude of the anterior mitral leaflet in early diastole (D-E interval) would be useful predictors of the pulmonary capillary wedge pressure (PCWP). We recorded M-mode mitral echograms and phonocardiograms in 33 patients (aged 38-70 years) with acute myocardial infarction (AMI) in the coronary care unit and in 34 patients (aged 40-75 years) with prior myocardial infarction (OMI) during cardiac catheterization. All patients underwent the insertion of a flow-directed pulmonary artery catheter to obtain the PCWP. We measured the IRT and the D-E interval from the phonocardiograms and the M-mode echograms. There was no significant correlation between the IRT and the mean PCWP (mPCWP) in patients with AMI and in patients with OMI. The D-E interval was significantly and inversely correlated with the mPCWP (r = -0.91, p < O.OOOl) in all patients. The regression equation was mPCWP = -0.42 × (D-E) +47.9. The D-E interval of ≤ 75 ms indicated a high mPCWP (mPCWP > 18 mm Hg) with high sensitivity (96%) and specificity (88%). The derived equation was tested in a prospective group of 32 additional patients (aged 43-75 years). A significant correlation was observed between the predicted and measured mPCWP (r =0.91, p < O.OOOl). Thus, the PCWP can be estimated by using the D-E interval derived from M-mode mitral echograms in patients in the coronary care unit and in patients with chronic heart disease.