Aims To assess the prevalence of heart failure and asymptomatic left ventricular systolic dysfunction in the chronically paced population. Methods and Results Three hundred and seven patients were identified from attendance at routine pacemaker follow-up clinic. Subjects underwent a medical history and examination, 6-minute walk test and echocardiography. 94 (31%) had a left ventricutar ejection fraction (LVEF) <40%, of whom 83 had symptoms of heart failure (70% NYHA II, 26% NYHA III and 4% NYHA IV). Heart failure was more prevalent in patients with single chamber compared to dual chamber pacemakers, (DDD(R) 18% vs 35% VVI(R), p<0.008), and those with chronic atrial. fibrillation (AF) compared to those with sinus rhythm (42% vs 21%, p=0.003). Decreasing 6-minute walk distance, history of ischaemic heart disease and years of pacing were independently associated with the presence of heart failure (combined R=0.572, p<0.001). Conclusions Heart failure due to left ventricutar systolic dysfunction is common in the paced population. Only a minority of these had a pre-existing diagnosis and a smaller proportion were on 'optimal' therapy. Echocardiographic screening of this high-risk population is justified to improve rates of diagnosis and treatment of heart failure. (C) 2003 Published by Elsevier Science Ltd on behalf of The European Society of Cardiology.