I understand that the combos work the best but the Serevent in Advair (or any long acting bronchodilator) can cause the rapid heartbeat or what I call "poundings" -- not necessarily rapid but strong heartbeats. I'm going to stick with the Pulmicort for awhile. I'm seeing a small improvement over the last few days. If the Symbicort works for you with no unpleasant side effects then that's great!