Background : Non-ischemic left ventricular systolic dysfunction is known to recover LV function in 25% of patients. However, the influential factor of severe left ventricular systolic dysfunction of unknown etiology is not well known. Methods : From January 1997 to June 2007, 60 consecutive patients with severe left ventricular systolic dysfunction of unknown etiology were enrolled. Severe left ventricular systolic dysfunction was defined as less than 35% of left ventricular ejection fraction(LVEF) and nearly normalized LVEF is defined as more than 50%. Results : 60 patients were followed for an average 49 months. 35 patients (15 males, mean age ; 54.7짹12.6 years) recovered to nearly normal LVEF (23.7짹3.8% at admission, 59.9짹5.9% at follow up) and 25 patients (19 males, mean age ; 57.1짹16.1 years) showed persistent LV systolic dysfunction (LVEF of 21.8짹5.0 % at admission , 31.9짹8.9% at follow up). There was no difference in the baseline clinical factor and medication including ARB or ACE inhibitor. However, Recovery of LV systolic function was more frequently observed in women, non-alcoholics and in patients with higher systolic blood pressure at admission. There was no significant difference in the incidence of all cause of death, non-fetal MI, readmission due to heart failure and cardiac death. Conclusion : Severe LV systolic dysfunction of unknown etiology can recover to nearly normal LV systolic function with proper medical treatment. We observed a tendancy of recovery of LV function in wemen, non-alcoholics, and in patients with hypertension at admission.