Abstract: Electrocardiography（ECG） before and after cardioversion of atrial fibrillation（Af） in 18 cases of hypertensive heart disease and Af was compared.It was found that QRS voltage was much lower in Af than in sinus rhythm,and Σ QRS decreased by 17.9% （182.5±40.7 vs 149.2±33.6 mm,P＜0.025）.Simultaneous echocardiography indicated that QRS voltage reduction in Af was related to the left ventricular volume decrease.This suggests that ECG standard for detecting left ventricular hypertrophy in Af should be reduced relevantly,or it would influence the sensitivity.