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Objectives: Ejection fraction (EF) reaction upon exercise by radionuclide ventriculography and standard echocardiographic parameters was evaluated as predictors for post-operative left ventricular (LV) function in chronic aortic regurgitation (AR). Background: The optimal timing of surgery for chronic AR is when the left ventricle is still compensating for the volume and pressure overload without irreversible dysfunction. For asymptomatic patients when EF is normal and LV diameters are borderline, exercise testing is recommended by present guidelines. However, only a limited number of studies have been performed, and data are scarce on this subject. Methods: Radionuclide ventriculography with multiple gated acquisition at rest and during exercise was performed in 29 consecutive patients with severe chronic aortic regurgitation pre-operatively and 6 months post-operatively. Patient subgroups were formed based on pre-operative EF exercise response (ΔEF) and were categorized as decreasing (ΔEF <−5%), unaltered (−5% ≤ ΔEF ≤ 5%), and increasing (ΔEF > 5%). A 5% or higher increase was considered normal. The LV diameters and mass were measured by echocardiography. Results: Pre-operative LV diameters were markedly elevated before surgery and diminished significantly after surgery. Left ventricular diameters, LV mass, EF at rest (EFrest), and EF change from rest to exercise (ΔEF) were independent of New York Heart Association functional class. Pre-operative end-diastolic diameter proved to be a predictor for pre- and post-operative ΔEF (p = 0.003; p = 0.04) but not for the nature of the exercise response post-operatively. Patients with decreasing and unaltered EF pre-operatively presented a significantly higher but still abnormal ΔEF post-operatively. Those with increasing EF pre-operatively had a similar response and a normal ΔEF post-operatively. Pre-operative ΔEF was not only a predictor for post-operative ΔEF (p = 0.02) but also classified patients into post-operative subgroups (EF decreasing, p = 0.03; unaltered, p = 0.02; increasing, p = 0.0008). Conclusions: An abnormal EF response to exercise may also occur in patients who do not fulfill criteria for surgery based on LV dimensions or EF. A follow-up of exercise LV function and adjusting the timing of surgery according to the nature of exercise response could, therefore, be beneficial. [Copyright &y& Elsevier]