Sick sinus syndrome is a syndrome that describes a group of arythmia characterized by a failure of the sinus node, the part of the heart that sets the steady pace described as sinus rhythm. It's underlying causes are unknown, but it tends to occur in the elderly. It can also appear in persons who have had heart surgery, and often appears together with other issues of the heart, such as coronary artery disease, high blood pressure, and heart valve disorders. It can also appear in any patient who is suffering from another disease that affects the structure of the heart, such as sarcoidosis and amyloidosis