Background : Incessant tachyarrhythmia is one of the etiology of LV systolic dysfunction(Tachycardia induced cardiomyopathy, TCM). TCM need to aggressive treatment to improve heart failure, but the index is limited to differentiate TCM from other causes of cardiomyopathy. Method: The subject group was 25 patients (male 15, mean age 62.0+/-12.9) who admitted as dilated cardiomyopathy with 1) heart rate more than 120/min, 2) symptoms less than 3 months, 3) no LVH in ECG and 4) increase of LV wall excursion after postectopic beat. Serial echocardiogram, ECG, history taking and physical examination were obtained at discharge and 1, 3, 6, 9. 12 month later. Result: The term of follow-up was 10.6+/-2.2(4-39) months, causes of tachyarrhythmia were chronic atrial fibrillation in 19 patients (76%), 2(8%) of atrial flutter and sinus tachycardia, 1(4%) of paroximal atrial fibrillation and multiple atrial tachycardia. Comorbid diseases were hypertension in 9 patients, chronic obstructive pulmonary disease in 3 patients, hyperthyroidism in 1 patient. 10 patients with atrial fibrillation received amiodarone, 5 patients received amiodarone with cardioversion. 2 patients with atrial flutter were placed under cardioversion. 4 patients conversed sinus rhythm or slower heart rate by treatment of comorbid disease. One patient with severe pulmonary disease expired in state of tachyarrythmia. 3 patients with COPD and 1 patient who discontinued the medication recurrd the tachyarrythmia. After reinstitution of amidalone LV function was recovered. 4 patient (16%) who took the amiodarone more than 6 months had not recurred the arrhythmia and LV dysfunction. Conclusion: The represented index is useful for the prediction of tachycardia induced cardiomyopathy. The prognosis of TCMP is good relatively, recovered LV function is maintained and the comorbid disease influenced long term survival.