The diagnostic usefulness of the mitral E/E' ratio (derived from tissue Doppler imaging) as an estimate of left ventricular filling pressures was studied in 28 patients with diastolic heart failure (defined by heart failure signs and symptoms but with preserved ejection fraction) and in 46 patients with systolic heart failure (heart failure signs and symptoms and reduced ejection fraction). E/E' was reflective of filling pressures in subjects with diastolic and systolic heart failure and may be of special use in ruling out elevated filling pressures in subjects with suspected diastolic heart failure.