Atrial fibrillation is an irregular heart beat caused by irritability and abnormal electrial activity in the atrium of the heart. It can cause fainting spells and a very fast heart beat which can be treated with medications. It can also cause strokes and some patients may require blood thinner medications to prevent this.If you have history of a. fib. please let us know before surgery. If you are taking any medications for a. fib. we need to know that long before surgery because you may be on a blood thinner. We need to determine if your blood thinner can be safely stopped for the time around your surgery.