Whether retrograde coronary sinus cardioplegia adequately preserves right ventricular (RV) function is still a point of concern. Using technetium Tc 99m-labeled red blood cells, we assessed global and segmental RV function by first-pass and gated blood-pool radionuclide angiocardiography before and within 24 hours after aortic valve replacement in 14 consecutive patients (age, 58 ± 5 years, mean ± SEM). Coronary sinus cardioplegia was given in a multidose fashion at a flow rate of 50-70 ml/min through a balloon-tipped cathether, with the inflated balloon kept seated around the intra-atrial rim of the coronary sinus orifice. Additional myocardial protection was provided by systemic (25°C) and topical hypothermia. Postoperatively, none of the patients had clinical or hemodynamic patterns suggestive of RV dysfunction. The postoperative global RV ejection fraction (0.49 ± 0.03) was similar to the preoperative value (0.49 ± 0.01). Analysis of segmental wall motion did not reveal postoperative abnormalities of new onset in any of the three anatomically defined RV regions (free wall, apex, and septum). Similarly, RV end-diastolic and end-diastolic and end-systolic volume indexes (ml/m2) were not significantly affected by coronary sinus cardioplegia, being 71.6 ± 5.8 and 36.1 ± 3.5 before, and 67.4 ± 3.8 and 34.5 ± 2.3 after aortic valve replacement, respectively. We conclude that retrograde coronary sinus cardioplegia does not cause a detectable impairment of RV function if the balloon catheter does not obstruct the terminal tributaries of the coronary sinus and, hence, does not impede delivery of cardioplegia to right-sided cardiac structures.