What are the known side effects of azithromycin?

The major concern about azithromycin is its potential to cause changes in the electrical activity of the heart that may lead to arrhythmias, or irregular heart rhythms. This condition can cause sudden cardiovascular death, or a heart attack. Azithromycin is also known to cause QT interval prolongation, or a longer-than-normal time between two specific measurable points in a heartbeat. This, too, can lead to fatal heart problems.