“During atrial fibrillation, the heart’s two upper chambers (the atria) beat chaotically and irregularly — out of coordination with the two lower chambers (the ventricles) of the heart.  Sometimes the misfiring signals can also make your heart’s two bottom chambers, called ventricles, beat too quickly. That’s a specific type of atrial fibrillation called AFib with rapid ventricular response.  Any type of AFib can lead to a stroke or heart failure. If you don’t get treated, over time the condition can damage your heart muscle and lead to heart failure.”.

WebMD