summaryBackground: Previous retrospective studies could find a predominant incidence of coronary sinus (CS) anomalies in patients with accessory pathways and a characteristic anatomy of the CS ostium in patients with atrioventricular nodal reentrant tachycardias (AVNRT).Hypothesis: In the present prospective study, CS angiograms were prospectively performed to analyze the incidence of CS anomalies and to measure the diameters of the CS ostium.Methods: The study included patients referred for electrophysiologic study and catheter ablation of various tachyarrhythmias. The anatomy of the CS and its side branches was visualized [left anterior oblique (LAO) 30°, right anterior oblique (RAO) 30"] by retrograde angiography in 204 con-