Does alieve have any unacceptable side effects for a senior with afib?

Yes.: If you mean "Aleve" the non-steroidal anti-inflammatory medication, it could predispose to stomach irritation and bleeding, and an increase in blood pressure. Many patients with A. fib are on blood thinners, and if you are, there is an increased risk of bleeding. Please discuss this with your doctor. He will know what other medications you are on and advise you accordingly.

Yes: With A fib you should be on an anticoagulant and any NSAID (Aleve) can either interfere with the beneficial effect of, or exacerbate the risk of the anticoagulant. Tylenol should be fine but I would check with your cardiologist for recommendations