Sick sinus syndrome is an abnormality of the natural pacemaker of the heart, the sino-atrial node (also known as sinus node and SA node). The automaticity of the sinus node is reduced in sick sinus syndrome, leading to bradycardia and long pauses. The person may develop syncope due to the low heart rate. In some persons it is associated with disease of the atrio-ventricular (AV) node as well. In certain cases, there is intermittent tachycardia along with bradycardia. Then it is known as tachy-brady syndrome. Symptomatic sick sinus syndrome needs a pacemaker implantation.