I was on verapamil for many years and didn't have SVTs for five years and then whammo. So the cardio put me on atenolol 25mg at night and it made me dizzy and whoozy that I had to miss a day of work. The switched me to diltiazem and it helped. I would reconfirm with your doc and just make sure someone is nearby. What my doc said is that it could lower my bp and heartrate too low and cause me to passout.