Hello welcome to HCM. I have gone through your description. Atrial fibrillation is fast irregular contraction of the upper chambers of the heart. Due to irregular heart rate, the atrial filling is impacted and hence some amount of blood always goes back into the lungs causing pulmonary edema or congestion in the lungs. This causes the breathlessness. The aim in AF is to control the rate of the lower chambers of the heart i.e. the ventricles. Flecainide helps in controlling the ventricular rate (while the atria still beat fast) and in treatment of AF. But in AF, due to irregular heart beats clots tend to form in the heart and when the patient goes into normal sinus rhythm these clots tend to embolize or migrate into the distal vessels i.e. the organs including the brain. This can cause symptoms of stroke and slurring of speech. Hence, in view of the above, he needs to be on diuretics (water pill) to decrease the fluid accumulation in the lungs and also on special blood thinners (anticoagulants) to prevent the formation of clots in the heart. In addition to Flecainide, diuretics and anticoagulants should be added. An MRI of the brain and chest X ray should be done to evaluate for stroke like symptoms and congestion in the chest. Wishing him good health Regards