One hundred sixty-nine patients undergoing coronary artery bypass grafting were included in a prospective study to test the effect of coronary pathology on conduction disturbances (CD). At the same time, several other proposed preoperative and intraoperative predictors of CD were collected. From the angiograms, the vascularization of the interventricular septum was classified according to Mosseri and colleagues. Ninety-four patients (56%) had type II coronary pathology, which does not allow full revascularization of the interventricular septum. The tested classification did correlate with the state of coronary disease, resulting in more left main coronary stenoses and more numerous peripheral anastomoses in type II patients. However, there was no correlation between the classification and CD. Patients with permanent CD (34%) had more left main coronary artery stenoses (29% versus 14%; p = 0.03). Their measured maximal myocardial temperatures were lower in all three myocardial regions measured (p = 0.01 to 0.07), and their creatine kinase MB fraction values on the day of operation were also higher (92 versus 70 IU; p = 0.002). In multivariate logistic regression analysis, the maximal temperature of the left circumflex artery region and the presence of left main coronary artery stenoses were the only independent predictors of permanent CD. We conclude that excessively low myocardial temperatures during cardioplegia may cause CD.