To determine the role of the sinus node artery and the clinical course in postmyocardial infarction sinus node dysfunction, 27 patients with acute inferior myocardial infarction and single-vessel coronary artery disease were studied. In 13 patients (group 1) the infarct-related coronary artery was occluded proximally and in 14 (group 2) distally to the site of origin of the sinus node artery. At electrophysiology, performed 10 +/- 3 days from the acute event, basal and intrinsic heart rate were lower in group 1 compared to group 2 patients (54 +/- 4.8 vs. 69 +/- 7 beats/min, p = 0.001, and 66 +/- 7 vs. 76 +/- 8 beats/min, p = 0.006, respectively) while basal and intrinsic corrected sinus node recovery times were prolonged in group 1 compared to group 2 patients (585 +/- 49.3 vs. 324 +/- 61.3 ms, p = 0.0001, and 601 +/- 39.1 vs. 335 +/- 73 ms, p = 0.0001). During a 6-month follow-up no episodes of dizziness, syncope or angina were reported. Moreover, at the end of follow-up resting heart rate (70 +/- 11 vs. 73 +/- 7 beats/min, nonsignificant), maximal exercise heart rate (166 +/- 19 vs. 170 +/- 23 beats/min, nonsignificant), and exercise time (491 +/- 120 vs. 480 +/- 155 s, nonsignificant) were similar between the two groups and no exercise-induced ischemic ST segment depression was observed. Sinus node dysfunction in patients with inferior myocardial infarction and one-vessel disease is related to the occlusion of the infarct-related coronary artery proximal to the site of origin of the sinus node artery and is not associated with increased cardiovascular morbidity in the first 6 months from the acute event.