BACKGROUND PQ segment deviation is almost as characteristic as the classic ST segment deviation and is detected in most patients with pericarditis. However, as infarction-associated pericarditis remains over the infarct zone, PQ segment depression is observed much less often in patients with acute myocardial infarction. RESULTS We designed this study to examine the clinical significance of PQ segment depression in acute Q wave inferior myocardial infarction. We examined 171 consecutive patients with acute Q wave inferior myocardial infarction by means of auscultation, ECG, and two-dimensional echocardiography. The diagnosis of pericarditis was made on the basis of pericardial rub detected by more than two observers during the first 3 days after admission. At least 0.5 mm of PQ segment depression from the TP segment lasting more than 24 hours in both limb and precordial leads was considered diagnostic of PQ segment depression. CONCLUSIONS PQ segment depression was present in 14 patients and absent in 157 patients. Eleven patients with and 55 patients without PQ segment depression had advanced asynergy (akinesis or dyskinesis) in the posterior segments, whereas 9 patients with and 20 patients without PQ segment depression had pericardial rub. When multivariate analysis was performed to determine the important variables related to the occurrence of PQ segment depression, pericardial rub was selected with advanced asynergy of the posterior segment as significant factors related to PQ segment depression. Major complications (ventricular fibrillation, sustained ventricular tachycardia, cardiogenic shock, need for pacing) were present in 63 patients; 9 with (64%) and 54 without (34%) PQ segment depression. PQ segment depression was one of the clinical signs of more extensive damage extending to the posterior segments and increased incidence of major complications.