OBJECTIVES: This study aimed to investigate the relationship between left ventricular (LV) remodelling and systolic function in high-gradient severe aortic stenosis (AS) using cardiovascular magnetic resonance (CMR) imaging. Patients with low ejection fraction (left ventricular ejection fraction (LVEF) <50%) high-gradient severe AS (low ejection fraction high-gradient (LEF-HG)), that is, afterload mismatch, were compared with patients with normal ejection fraction high-gradient (NEF-HG) severe AS. The hypothesis of insufficient left ventricular hypertrophy (LVH) leading to high wall stress as the mechanism of systolic dysfunction in afterload mismatch was tested. DESIGN: This was a cross-sectional study design. SETTING: The study was performed at a single tertiary academic hospital in the Western Cape, South Africa. PARTICIPANTS: A total of 48 participants with high-gradient (mean gradient ≥40 mm Hg) severe AS (aortic valve area (AVA) <1.0 cm2) were consecutively recruited. Of 48 participants, 24 (50%) had LEF-HG AS (mean AVA 0.52±0.18 cm2, mean gradient 54 (21) mm Hg, mean LVEF 29±11%). The remainder of the cohort had NEF-HG AS (mean AVA 0.70±0.17 cm2, mean gradient 53 (25) mm Hg, LVEF 64±14%). RESULTS: End-systolic wall stress (ESWS) was higher in the LEF-HG group (265.3±83.5 vs 122.8±54.7×103 dynes/cm2; p<0.0001) and associated significantly with LVEF. The degree of LVH measured by wall thickness (13.0 vs 13.0 mm, p>0.99) was identical between the groups. The LV mass index was numerically higher in the LEF-HG group (101.9±37.2 vs 77.6±22.2 g/m2) but this was not statistically significant (p=0.91). The LEF-HG AS group demonstrated significant LV cavity dilation (LV End-Diastolic Volume Index 124.9±29.9 vs 78.4±16.0 mL/m2, p<0.0001). Elevated ESWS was associated with smaller valve areas and cavity dilation but not with LVH. CONCLUSION: The reduced LVEF in afterload mismatch was associated with high ESWS as previously suggested. However, insufficient concentric LVH was not observed in LEF-HG AS and therefore not associated with high ESWS. LV cavity dilation and smaller valve areas were instead associated with the elevated ESWS in afterload mismatch, which may represent the decompensated stage of high-gradient severe AS.