According to the recent concept, heart failure has been regarded as the syndrome in which left ventricular function is associated with shortened life expectancy. Thus, an understanding of heart failure is of the utmost importance in understanding the mortality. Five primary factors that appear to influence prognosis in heart failure are an etiology of heart failure, the severity of ventricular dysfunction, the degree of impairment of exercise capacity, the activation of neurohumoral factors, and high incidence of ventricular arrhythmias. Both left ventricular ejection fraction and exercise tolerance bear a close relationship to survival in heart failure but there is only weak correlation between these two parameters indicating that each factor may be an independent determinant of survival. Sympathetic stimulation could certainly increase the likelihood of lethal ventricular arrhythmias and contribute to sudden death in heart failure. However, the result of recent large scale trials have indicated that reduction of mortality in patients with chronic heart failure and low ejection fraction by medical treatment was not necessarily a result of the reduced mortality due to an arrhythmia but that due to progressive heart failure. Establishing the prognosis of a patient with heart failure may be of considerable importance in patient management.