Many patients with heart failure exhibit a distinctive abnormal cyclical breathing pattern, 'periodic breathing'. This means that patients have a worse prognosis and they have debilitating symptoms including breathlessness, fatigue and disrupted sleep. Many of these patients also have cardiac pacemakers fitted, to improve their heart function. We have discovered a new physiological mechanism linking the heart and lungs, and have shown that by changing the programmed settings of a cardiac pacemakers, we can change a patient's breathing. If we increase the programmed pacing heart rate, we increase the rate of delivery of carbon dioxide to the lungs temporarily, which increases ventilation. When we reduce the programmed pacing heart rate, the converse happens. We aim to demonstrate this phenomenon scientifically, and to use this information to stabilise periodic breathing in heart failure patients using pacemakers. We then plan to continue to investigate whether we can show that sleep quality is improved in heart failure patients with periodic breathing, by our pacing protocol.