What is Atenolol ? I have taken 50 mg daily (1) for past 20 years, prescribed for occasional fast heart beat (comes on suddenly usually after a burst of adrenalin or sudden stress. Best to take it in advance. Taken it in advance will most of the time give you protection in preventing the occurance. No significant side effects. Good at lowering tension? Yes, in that it helps you to relax and know that you are not likely to have tachcardia (fast heart beat which comes on suddenly) thus allowing you to be more relaxed. Not sure your doctor would want you to use it occasionally but you should be clear with him and get his direction on that. Good luck. I attribute my long life in some part to atenolol---