Coronary sinus catheterization is important in electrophysiologic study of patients with supraventricular tachycardia. It can provide an anatomic guide for localization of slow atrioventricular nodal pathway and accessory pathways in the posteroseptal area and left-sided atrioventricular ring. However, the morphologic features of the coronary sinus and its significance in patients with supraventricular tachycardia have not been determined. Four hundred eight patients with accessory pathway-mediated tachyarrhythmia and atrioventricular nodal reentrant tachycardia underwent coronary arteriography for a coronary sinus venogram before electrophysiologic study and radiofrequency ablation. The venous phase of left coronary arteriography that delineated the morphologic features of the coronary sinus was carefully evaluated and recorded in multiple projections. Major coronary sinus abnormalities were defined, and they were found in 12 patients (2.9%). Six patients had angulation of the coronary sinus, 4 patients had hypoplasia of the coronary sinus, 1 patient had narrowing of the proximal coronary sinus, and 1 patient had a fistula from persistent left superior vena cava to the coronary sinus. Of 175 patients with atrioventricular nodal reentrant tachycardia, only 1 patient had major coronary sinus abnormalities (proximal angulation), whereas of 233 patients with accessory pathway-mediated tachycardia, 11 patients had major coronary sinus abnormalities (0.6% vs 4.7%, p < 0.05). The accessory pathways in patients with major coronary sinus abnormalities were located exclusively in the left free wall and posteroseptal area. Proper coronary sinus catheterization could be accomplished in 396 patients with a normal coronary sinus, whereas it could be accomplished in only 1 of the 12 patients with major coronary sinus abnormalities (396/396 vs 1/12, p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)