Abstract: AIM To study the different effects of angiotensin Ⅱ type Ⅰ receptor antagonist and angiotensin conversion enzyme inhibitor on the p wave dispersion in eletrocardiography in patients with essential hypertension. METHODS Forty-eight patients were divided into two groups randomly: one group was treated with candesartan 4 mg/d while the other group with enalapril 10 mg/d totally for 6 months respectively and the p wave duration and p wave dispersion were analyzed before and after the treatment. RESULTS After the treatment, the p wave duration and p wave dispersion in both groups of patients with essential hypertension decreased (P<0.05). Candesartan had more obvious effect on p wave dispersion compared with that of enalapril. CONCLUSION Candesartan is more effective than enalapril in preventing atrial fibrillation in patients with essential hypertension.