Coronary collateral circulation determines the severity of ischemic myocardial damage. Increased P-wave dispersion is an independent predictor for atrial fibrillation. Consistent evidence is little about the relation between coronary collateral circulation and arrhythmia risk. In this article, the effect of coronary collateral circulation on P-wave dispersion was evaluated. Collateral grade and P-wave dispersion were ascertained in 100 patients with >or=85% diameter stenoses in left anterior descending or right coronary arteries. Left ventricular function score was also determined in all patients. Coronary collateral circulation was absent in 32 patients, whereas 68 patients had coronary collateral circulation. Patients with collateral grade >or=1 had greater left ventricular function score than did patients with collateral grade 0 (P = .048). However, there was no significant difference between P-wave dispersion of patients with and without coronary collateral circulation (P = .45). The presence of coronary collateral circulation failed to exert a beneficial decreasing effect on P-wave dispersion.