Abstract： Background Patients with heart failure were candidates for cardiac resynchronization therapy (CRT)regardless of underlying aetiology. This study observed the effect of CRT in patients with ischaemic or nonischaemic cardiomyopathy.Methods One hundred and forty-two patients with refractory chronic heart failure and left bundle branch block received cardiac resynchronization therapy, 91 men and 51 women, average age 60 years. Left ventricular ejection fraction (LVEF) was severely depressed (mean 29%), left ventricular end diastolic diameter (LVEDD)enlarged (mean 72 mm) and QRS width was lengthened (mean 147 ms). Ninety-eight had nonischaemic cardiomyopathy and 44 had ischaemic cardiomyopathy.Results After cardiac resynchronization therapy, the heart function was significantly improved. The mean LVEF increased from 29% to 36% after pacing. In patients with nonischaemic cardiomyopathy, the LVEF was improved from 28% to 37%, and in patients with ischaemic cardiomyopathy, the LVEF was improved from 30% to 36%. No significant difference of the improvement was found between the two groups (P＞0.05).Conclusions Cardiac resynchronization therapy could significantly improve cardiac function in patients with chronic heart failure regardless of the underlying heart disease.