Purpose: The myocardial damage was occurred after attack in patients with paroxysmal atrial fibrillation (PAF). The aim of this study was to evaluate the determinant to elevate the cardiac enzyme after attack in patient with PAF. Methods: We enrolled 127 patients with paroxysmal attack of AF and terminated spontaneously or by cardioversion within 7 days. The myocardial damage was defined as elevated CK-MB or troponin I. We divided two groups into elevated cardiac enzyme group (52 patients, 65.9짹12.1yr) and normal group (75 patients, 59.8짹15.7 yrs). We measured the C-reactive protein (CRP), pro-brain natriuretic peptide (pro-BNP), thyroid related hormone like thyroid stimulating hormone (TSH), T3 and free T4, left ventricular ejection fraction (LVEF), left atrial diameter (LAD) and ventricular rate during AF. Results: The patients with elevated cardiac enzyme group were older, lower TSH level, higher CRP and pro-BNP level and larger LAD compared to those with normal group. Multiple logistic regression analysis showed that level of TSH and LVEF were independent predictors of elevated cardiac enzyme (p=0.010, Odd ratio 1.138, CI 1.032-1.256) after adjustment of age, log CRP, TSH, ventricular rate during AF and HTN. Conclusions: The larger LA size might be associated with transient myocardial damage following paroxysmal attack of AF. However, further larger study might be needed.