Anticoagulants (blood thinners) prevent blood clots from forming or growing. They are important for people with heart failure, as they often form blood clots in the heart or blood vessels. For patients with atrial fibrillation, i.e. irregular heart rhythm, which is common in heart failure, anticoagulants are vital because they prevent blood clots from forming in the left atrium. When a clot breaks away from the vessel wall, it can lead to a stroke.