side effects of atenolol

I recently started on atenolol.  After taking 50mg 1 time a day for two days, I had several episodes of my HR dropping to 38-40's and after a minute or two, it would race back up to almost 100. (Without atenolo, my HR is typical greater than 100.) My chest almost aches when this happens and it feels as though my heart beats much stronger. it has been about 3 weeks now and I only notice this happening a few times a week, when I am sitting or laying down and doing something quietly (watching tv, helping with homework) is this a common side effect of atenolol?  Is it dangerous?

[Flycaster305]

That is a very low heartbeat rate.  Yes, Atenolol does slow down the heart rate, and the fact that you heart responds with a fast heart beat indicates to me something called Brady-Tachy Syndrome.  I would certainly contact your doctor as soon as practical.  I'd also suggest you be careful when rising from a sitting or resting position, particularly when getting up from bed at night.  I'd sit on the side of the bed until you are sure you aren't light-headed.  
On the other side of the coin, 100 bpm is a very rapid heartbeat.  
I'd ask your doctor about wearing a 24 or 48 hour heart monitor, and having an  cardio electro-physicist read the results.
One last question... do you smoke?  That can raise the heart rate.

Keep us informed, you have brought up an interesting situation.

[Encephalomalcia]

I am wondering if you were to take the brand name "Tenormin" if you would get these effects?  Sometimes generics in heart medication have side effects.  Also, different brands of generics can cause problems.  When my Mom was on Atenolol, she had problems.  Then, she switched to Tenormin and the problems went away.  Brand name is best with heart medication.