premature ventricular depolarizations
"I'm a 50 something female and I've been taking Toprol XL 25mg once a day for about 10 years for PVC's. It has worked very well to control my racing heart that woke me up in the night. Occasionally I still feel the extra/skipped beats but they are no longer worrisome. 
For about the past year I have been experiencing some shortness of breath at rest. I am wondering if this is related to the medication. Does anyone have any ideas about this?"