We are looking to enrol 45 patients with heart failure and mild obstruction to the flow of air in their lungs. Patients will be randomised to either carvedilol or metoprolol (standard doses). Following a minimum of 2 weeks of therapy of study medication the patient will undergo a study day involving an assessment of their lung function, an assessment of their heart failure, a "living with heart failure" questionnaire, blood tests and blood pressure and heart rate readings.