More than ten million Americans have atrial fibrillation—a dangerous but highly treatable heart arrhythmia, also known as a-fib. The statistic comes from the University of California San Francisco and Journal of the American College of Cardiology. The number is triple estimates from two decades ago. The study reviewed medical records of two million patients who received diagnosis and care for a-fib. Authors say a-fib has a broad range of complications from shortness of breath and light-headedness to blood clots, stroke, chronic kidney disease, dementia and even heart failure. Fortunately, they say, atrial fibrillation is preventable, and early detection and appropriate treatment can substantially reduce adverse outcomes.