Beta-blocker treatment is known to improve survival from several cardiac diseases. Unfortunately, betablockers are usually avoided in patients with chronic obstructive pulmonary disease (COPD) because of concerns that they may make airflow obstruction worse. Therefore, patients with COPD are often deprived of the benefits of beta-blockers even though they have a very high risk of cardiac problems. Recent evidence suggests that beta-blockers may be safe and effective in lung disease but there have been no clinical studies to confirm this. This feasibility study will assess the safety and tolerability of metoprolol, a cardio-selective beta-blocker, in patients with exacerbations of COPD to determine whether a randomised controlled trial of beta-blockers should be conducted. The randomised study will provide a definitive answer on whether beta-blockers are safe and effective in patients with chronic obstructive pulmonary disease. It has the potential to transform treatment of COPD and widen the indications for beta-blocker treatment.