Sick sinus syndrome (SSS), is a group of abnormal heart rhythms (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's primary pacemaker.[1] Tachycardia-bradycardia syndrome is a variant of sick sinus syndrome in which the arrhythmia alternates between slow and fast heart rates. Tachycardia-bradycardia syndrome is often associated with ischemic heart disease and heart valve disease. Disorders that cause scarring, degeneration, or damage to the sinoatrial node can cause sick sinus syndrome, including sarcoidosis, amyloidosis, hemochromatosis, Chagas' disease,[3] and cardiomyopathies.[2] Abnormal heart rhythms are often caused or worsened by medications such as digoxin, calcium channel blockers, beta-blockers, sympatholytic medications, and anti-arrhythmics.Coronary artery disease, high blood pressure, and aortic and mitral valve diseases may be associated with sick sinus syndrome, although this association may only be incidental. The mechanism is related to delayed escape. Congenital SSS can be due to mutations of the gene responsible for formation of Alpha subunit of sodium channel (SCN5A). Artificial pacemakers have been used in the treatment of sick sinus syndrome. Bradyarrhythmias are well controlled with pacemakers, while tachyarrhythmias respond well to medical therapy. However, because both bradyarrhythmias and tachyarrhythmias may be present, drugs to control tachyarrhythmia may exacerbate bradyarrhythmia. Therefore, a pacemaker is implanted before drug therapy is begun for the tachyarrhythmia.