Atrial fibrillation is the most common sustained cardiac arrhythmia. It is characterized by multiple foci within the atria that fire continuously in a chaotic pattern, causing irregular atrial rhythm. Causes of atrial fibrillation can easily be remembered by a mnemonic PIRATES P - Pulmonary embolism I - Ischemic heart disease R - Rheumatic heart disease A - Atrial myxoma T - Thyrotoxicosis E - Ethanol S - Sepsis