To determine whether or not spironolactone can prevent or delay the occurrence of atrial fibrillation.

To determine whether or not adding spironolactone can prevent or delay the occurrence of paroxysmal atrial fibrillation in patients who have received propafenone treatment.

Inclusion criteria:

1. 18 to 80 Y/O,
2. Paroxysmal AF.

Exclusion criteria:

1. GPT>100 IU/L or tota bilirubin >2 mg/dl;
2. Creatinine > 2 mg/dl;
3. Serum potassium >= 5 mM;
4. Serum sodium <=130 mM;
5. Uric acid > 10 mg/dl。