Pre-operative end-systolic volume (ESV) is predictive of outcome after surgery for severe aortic regurgitation. ESV is influenced by body size and reflects function and afterload, but not pre-load. Left ventricular (LV) chamber size and function were measured in 40 patients (ages 10 to 64 years) by echocardiography before and 7 months after operation and expressed as z-scores in addition to simple indexing. A functional pre-load index, a marker of pre-load reserve, was calculated. Independent risk factors for post-operative LV dysfunction included higher post-operative ESV z-score (odds ratio [OR]: 3.3, p = 0.006) and lower functional pre-load index (OR: 0.3, p = 0.03). ESV per square meter had similar power to the ESV z-score. The ESV uncorrected for body size underestimated risk in smaller patients and overestimated risk in larger patients (p < 0.002). Pre-load reserve is an independent risk factor for LV dysfunction after aortic valve surgery in patients with severe aortic regurgitation. Failure to correct ESV for body size introduces systematic bias to risk assessment.