We want to study the effect of the combination of metoprolol (a beta-blocker) with formoterol (a beta-agonist) on long function in patients with Chronic Obstructive Pulmonary Disease (COPD). There are more and more clues that a beta-blocker, when well chosen and in the right dosage, won't harm the long function in patients with COPD. Since a beta-blocker can be a valuable addition to treating patients with heart problems we would like to see if this category of medication can be available for COPD patients in the future.