A heart rhythm disorder in which the heart's natural pacemaker doesn't work as it should.

Sick sinus syndrome is a type of heart rhythm disorder. It affects a group of cells at the top of the heart called the sinus node. The condition causes slowed, paused or otherwise irregular heartbeats. The risk rises with age.

Symptoms include fatigue, dizziness, shortness of breath and fainting. Symptoms may be mild, or they may come and go. Some people don't have symptoms.

Treatment may include medicines to slow the heartbeat and prevent blood clots. Most people with sick sinus syndromes need a permanent device called a pacemaker to help the heart beat correctly.