Impaired diastolic function is related to subjective symptoms, reduced exercise capacity, and poor prognosis in patients with congestive heart failure, and an angiotensin II type-I receptor blocker might have a beneficial effect on diastolic function in such patients with heart failure. A 53-year-old woman underwent valvuloplasty of the mitral valve and later presented with heart failure symptoms, including exertional dyspnea and easy fatigue. Although no pathological changes could be identified by radiography of the chest, electrocardiography, or routine echocardiography, the assessment of diastolic function with Doppler echocardiography revealed left ventricular diastolic dysfunction. Her neurohumoral parameters and left ventricular diastolic dysfunction improved after 1 month of treatment with Valsartan, an angiotensin II type-I receptor blocker, accompanied by improvement of her subjective symptoms. This case implies that angiotensin II type-I receptor blocker could improve left ventricular diastolic dysfunction and that Doppler echocardiography might be useful for detecting diastolic dysfunction in high-risk patients undergoing cardiac surgery.