(1) Patients with severe bradycardia: A heart rate below 40 beats per minute during the day can often cause symptoms such as dizziness, blurred vision, weakness angina or syncope, and usually requires a pacemaker. (2) Patients with atrioventricular block: Most patients with 2nd and 3rd degree AV block require pacemaker implantation. (3) Atrial fibrillation with slow ventricular rate: If the heart rate is sometimes fast and sometimes slow in atrial fibrillation. When the heart rate is fast, panic and dizziness are evident, medication must be used to lower the heart rate, and if the heart rate itself is sometimes slow, for example, below 40 beats per minute, a pacemaker must generally be implanted.