Accurate assessment of pulmonary capillary wedge pressure (PCWP) is essential for physicians to effectively manage patients with acute decompensated heart failure. The ratio of early transmittal velocity to tissue Doppler mitral annular early diastolic velocity (E/E′) is used to estimate PCWP noninvasively in a wide range of cardiac patients. However, it remains contentious as to whether mitral E/E′ is a reliable predictor of PCWP. In the present study, acute heart failure patients were divided into two groups on the basis of left ventricular (LV) systolic function: those with preserved ejection fraction (HFpEF) and those with reduced ejection fraction (HFrEF). The usefulness of mitral E/E′ in estimating PCWP was compared between the two groups. Fifty consecutive patients who were admitted with acute decompensated heart failure and underwent both right-sided cardiac catheterization and transthoracic echocardiography during hospitalization were analyzed retrospectively. Pearson’s correlation was used to evaluate associations between Doppler parameters and PCWP. E/E′ was positively correlated with PCWP (r = 0.56, P = 0.01) in the heart failure with preserved ejection fraction group. However, no significant relationship was observed between PCWP and mitral E/E′ (P = 0.85) in the heart failure with reduced ejection fraction group. There were no significant correlations between any of the conventional parameters considered (LVEF, left atrial dimension, E/A, IVRT, and DT) with PCWP in either group. In conclusion, mitral E/E′ is useful for estimating PCWP in patients with acute heart failure with preserved ejection fraction but may not in those with reduced ejection fraction.