Sick sinus syndrome (SSS), also known as sinus node dysfunction, is a relatively rare type of arrhythmia (abnormal heart rhythm). It is a condition in which the sinus node, which is located in the right atrium and serves as the heart’s natural pacemaker, is unable to set the pace of the heart as well as it should. Sick sinus is a syndrome, or a cluster of signs and symptoms that occur together, whether or not the cause of the condition is known.

Men and women of all ages can develop SSS, but it is rarely diagnosed in people under age 50. While it is rare in children, the condition may develop in pediatric patients who have had open-heart surgery, particularly after surgery to the atria (upper chambers of the heart). SSS develops over a period of years, and it can often be difficult to recognize until it is in its advanced stages.

Advanced SSS is often marked by alternating rapid and slow heart rhythms, neither of which produces a good cardiac output. Patients can often feel this yo–yo effect, which results in not enough blood circulating through the body. If left untreated, sick sinus syndrome can lead to heart–related complications such as heart failure. In addition, patients with SSS are at increased risk for heart attack, even after treatment. However, treatment for the disease dramatically lowers risk of complications.