We investigated whether anti-tachycardia therapy might improve the altered cardiac adrenergic and systolic function in tachycardia-induced cardiomyopathy (TC) in contrast to dilated cardiomyopathy (DCM). The subjects were 23 patients with heart failure, consisting of 8 patients with TC (43.6 +/- 10.0 yrs) and 15 with DCM (45.3 +/- 8.2 yrs). TC was determined as impairment of left ventricular function secondary to chronic or very frequent arrhythmia during more than 10% of the day. All patients were receiving anti-tachycardia treatment. Cardiac 123I-MIBG uptake was assessed as the heart/mediastinum activity ratio (H/M) before and after treatment. LVEF was also assessed. In the baseline study, H/M and LVEF showed no difference between TC and DCM (2.21 +/- 0.44 vs. 2.10 +/- 0.42, 35.3 +/- 13.1 vs. 36.0 +/- 10.9%, respectively). After treatment, the degree of change in H/M and LVEF differed significantly (0.41 +/- 0.34 vs. 0.08 +/- 0.20, 20.5 +/- 14.4 vs. -2.1 +/- 9.6%, p < 0.01). In TC, heart failure improved after a shorter duration of treatment (p < 0.05). In conclusion, anti-tachycardia therapy can improve altered cardiac adrenergic function and systolic function in patients with TC over a shorter period than in those with DCM.