Atrial fibrillation has two very serious complications: stroke and heart failure. A stroke can occur if the irregular rhythm of your heart keeps it from pumping blood out of your upper heart chambers, the atria. As the blood collects in your atria, it can clot; the risk of blood clots is that they can get out of the heart, circulate through your body, and travel to your brain, where it can block blood flow - this is a stroke. Old age, high blood pressure, enlarged left atrium, diabetes, and structural heart disorders raise your risk for a clot. Stroke is such a risk in atrial fibrillation that many treatment plans include a medication to prevent clotting.
Heart failure can occur due to prolonged atrial fibrillation, which decreases the heart's ability to function. Untreated atrial fibrillation is more likely to cause heart failure. Discuss treatment options with your doctor that will reduce your risk for complications.