Irregular heart rates and rhythms (arrhythmias) occur commonly in the first week after heart surgery. They are associated with increased risks for stroke, heart attack, and death. They can increase postoperative care needs, length of hospital stay, and costs. Doctors usually give patients undergoing heart surgery beta-blocker drugs to help prevent dangerous heart rates and their complications. Another drug that they might consider giving is amiodarone. Amiodarone works by slowing down the electrical signals in both the upper chambers (atria) and lower chambers (ventricles) of the heart.