The effect of cardiac resynchronization therapy (CRT) on right ventricular (RV) function has not been well described. The purpose of this study was to use tissue Doppler imaging to assess changes in RV function after CRT. Thirty-five patients with heart failure (age 65 +/- 10 years; 26 men) who underwent color tissue Doppler imaging of the right ventricle both immediately before CRT and >3 months (mean 6 +/- 3) after were studied. Myocardial systolic velocity was measured at the tricuspid annulus and basal and midventricular segments of the right ventricle free wall and averaged to obtain a measure of global RV function (RV S(m)). Left ventricular ejection fraction was also measured using biplane Simpson's method before and after CRT. RV S(m) significantly improved after CRT (5.4 +/- 1.9 to 7.1 +/- 2.6 cm/s; p <0.001), as did left ventricular ejection fraction (26 +/- 6% to 34 +/- 10%; p <0.001). Twenty-one of 35 patients (60%) showed an increase in RV S(m) > or =1 cm/s, with an increase > or =2 cm/s in 13 of those patients (37%). Improvement was seen in both ischemic and nonischemic patients and was independent of improvement in left ventricular ejection fraction and baseline left ventricular dyssynchrony. In conclusion, CRT resulted in improved RV function measured as RV S(m). CRT had beneficial effects on RV function independent of improvement in left ventricular ejection fraction.