The purpose of this study was to evaluate QRS width as an indication for cardiac resynchronization therapy. This study group consisted of 64 heart failure patients (51 men, age average 60.5 +/- 15.5 years) with a left ventricular ejection fraction (LVEF) of less than 35%. Patients were divided into two groups according to their QRS width; the wide QRS group (QRS width greater than or equal to 120 ms, 31 patients) and the narrow QRS group (QRS width less than 120 ms, 33 patients). The ventricular dyssynchrony (VD), i.e., the inter- and intraventricular dyssynchrony, of the two groups was compared. The correlation between QRS width and VD was evaluated in all patients. There were no significant differences between the wide and the narrow QRS groups concerning interventricular dyssynchrony [28.4 +/- 26.1 ms vs. 25.3 +/- 18.2 ms, not significant (NS)] or intraventricular dyssynchrony (99.0 +/- 43.8 ms vs. 109.0 +/- 56.6 ms, NS). Nor were there any differences in the LVEF (26.6 +/- 6.6% vs. 28.2 +/- 5.1%, NS), brain natriuretic peptide (BNP) (567.0 +/- 319.0 pg/ml vs. 390.0 +/- 375.8 pg/ml, NS), and New York Heart Association (NYHA) class (2.4 +/- 0.8 vs. 2.0 +/- 1.0, NS). QRS width did not correlate with interventricular (r = 0.026, NS) or intraventricular dyssynchrony (r = 0.052, NS). There were no differences in VD between the two groups based on differences in QRS width. There was also no correlation between QRS width and VD. It is suggested that QRS width is not an absolute indication for cardiac resynchronization therapy.