What complications can arise from untreated atrial fibrillation?

Untreated atrial fibrillation can lead to significant complications due to its effects on blood flow and the heart's function. One of the most serious outcomes is the increased risk of stroke, which occurs because blood can pool in the atria of the heart, forming clots that can travel to the brain. Additionally, atrial fibrillation can also contribute to heart failure. The irregular and often rapid heart rate associated with this condition may weaken the heart over time, making it less effective in pumping blood to meet the body's needs.

Other options do not accurately capture the complications associated with your question. For instance, decreased blood pressure is not a primary complication of untreated atrial fibrillation; rather, blood pressure may vary depending on other factors. Improved exercise tolerance and decreased heart rate are also not effects of untreated atrial fibrillation. In fact, patients often experience reduced exercise capacity and an increased heart rate, further complicating their situation. Therefore, the increased risk of stroke and heart failure is indeed the most relevant complication linked with untreated atrial fibrillation.