Left and right bundle branch block (LBBB and RBBB) may be present in the absence of significant heart disease. In middle aged and older patients an underlying cardiac pathology is, however, often present. LBBB is more commonly associated with heart disease than RBBB. If a patient with a newly diagnosed bundle branch block is asymptomatic, has no signs suggestive of heart disease and echocardiographic findings are normal it may be concluded that no cardiac pathology is present. Nevertheless, the continuing monitoring of these factors is important. The significance of left anterior hemiblock (LAHB) is slight as far as prognosis is concerned. Bifascicular and trifascicular block, even if asymptomatic, are an indication for follow-up observation with clinical check-ups and ECG recordings.