Complications

Doctors can manage the symptoms of Kawasaki disease if they catch it early. The symptoms typically disappear within just two days of when treatment begins. Usually, if Kawasaki disease is treated within 10 days of when the first symptoms begin, no heart problems develop.

But if the illness goes untreated (time period can vary, but likely for 10-14 days and sooner in young infants), it can lead to more serious complications that involve the child's heart. The coronary arteries are most often affected. Part of a coronary wall can be weakened and balloon (bulge out) in an aneurysm. A blood clot can form in this weakened area and block the artery, sometimes leading to a heart attack. The aneurysm can also burst, but this rarely happens.
Other changes include inflammation of the heart muscle (myocarditis) or the sac surrounding the heart (pericarditis). Arrhythmias (abnormal heart rhythms) or abnormal functioning of some heart valves also can occur.

Usually all the heart problems go away in five or six weeks, and there's no lasting damage. Sometimes coronary artery damage persists, however.