As you have already understood that your heart was enlarged before surgery and you are suffering from chronic atrial fibrillation. This has to be controlled. The present drugs that is Aten and Dilguard are quite efficient in controlling your AF. The aim of the treatment is to keep the heart rate within normal range which is done well by the above two drugs and since you have a what I believe is a mechanical prosthetic valve, anticoagulation, that is with Tab. Acitrom should be life long. So just relax and take regular medication and be under your cardiologists follow up regularly.