Atrial fibrillation is a serious condition because it can result in an increased risk of blood clots being formed. It is important that the atria contract properly to make sure all the blood is pushed into the ventricles, but in atrial fibrillation this may not happen and blood may pool in the atria increasing the chance of clots forming. It also can lead to heart failure since the heart has to work harder to get the job done, and there is an increased risk of strokes because of the propensity to throw blood clots.