Atrial fibrillation patients often have a longstanding history of untreated high blood pressure, which leads to a thickening of the ventricle and a pressure overload in the atria. In one case, a 75-year-old woman with atrial fibrillation presented with an irregular heartbeat and low blood pressure. Doctors shocked her heart to restore normal rhythm; she was then placed on medication to reduce her risk of another episode and to prevent stroke.