Sick sinus syndrome is a rare cardiac rhythm disease, usually of the elderly, characterized by electrocardiographic findings of sinus bradycardia, atrial fibrillation, atrial tachycardia sinus arrest, or sino-atrial block, and that manifest with symptoms like syncope, dizziness, palpitations, fatigue, or even heart failure. It results from malfunction of the cardiac conduction system, probably secondary to degenerative fibrosis of nodal tissue in the elderly or secondary to cardiac disorders in younger patients. The disease is MONDO_0012061 (familial sick sinus syndrome). Also known as: familial sinus node dysfunction, hereditary sick sinus syndrome.