Background: The ratio of early transmitral velocity to early diastolic velocity of the mitral annulus (E/E’) has been shown to be an excellent predictor of left ventricular filling pressure. However, the clinical significance of mildly elevated E/E’ (8≤E/E’≤15) remains to be clarified. Left atrial (LA) volume would reflect the duration and severity of left ventricular diastolic dysfunction. There is a graded relation between LA volume index (LAVI) and severity of diastolic dysfunction. Purpose: We hypothesized that LAVI could be useful for predicting increased PAWP in coronary heart disease patients with mildly elevated E/E’. Subjects and Methods: Patients admitted to the coronary care unit at our hospital who had indwelling pulmonary artery catheters were eligible. Fifty-eight patients without atrial fibrillation or severe mitral regurgitation underwent echocardiography (Sonos 5500 or 7500; S3 probe; Philips). Tissue Doppler imaging of the mitral annulus was also obtained. Early diastolic E’ velocity was measured from the septal mitral annulus velocity profile in the apical 4-chamber view. LA volume was assessed by the biplane Simpson’s method from apical 4- and 2-chamber views in end systole. LAVI was obtained by correcting for body surface area. PAWP was measured simultaneously in all the patients. Results: In 23 patients with mildly elevated E/E’ (8≤E/E’≤15) , there was no correlation between PAWP and E/E’ (p=0.40). However, LAVI positively correlated with PAWP in those patients (r=0.64, p<0.001). LAVI≥32ml/m2 was the optimal cutoff to predict PAWP≥15mmHg (sensitivity 72%, specificity 80%). Conclusion: LAVI could be a useful adjunct measure for predicting increased PAWP in coronary heart disease patients with mildly elevated E/E’.