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Aims: The World Heart Federation (WHF) criteria identify a large borderline rheumatic heart disease (RHD) category that has hampered the implementation of population-based screening. Inter-scallop separations (ISS) of the posterior mitral valve leaflet, a recently described normal variant of the mitral valve, appears to be an important cause of mild mitral regurgitation (MR) leading to misclassification of cases as WHF 'borderline RHD'. This study aims to report the findings of the Echo in Africa project, a large-scale RHD screening project in South Africa and determine what proportion of borderline cases would be re-classified as normal if there were a systematic identification of ISS-related MR., Methods and Results: A prospective cross-sectional study of underserved secondary schools in the Western Cape was conducted. Participants underwent a screening study with a handheld (HH) ultrasound device. Children with an abnormal HH study were re-evaluated with a portable laptop echocardiography machine. A mechanistic evaluation was applied in cases with isolated WHF 'pathological' MR (WHF 'borderline RHD'). A total of 5255 participants (mean age 15± years) were screened. A total of 3439 (65.8%) were female. Forty-nine cases of WHF 'definite RHD' [9.1 cases/1000 (95% confidence interval, CI, 6.8-12.1 cases/1000)] and 104 cases of WHF 'borderline RHD' [19.5 cases/1000 (95% CI, 16.0-23.7 cases/1000)] were identified. Inter-scallop separations-related MR was the underlying mechanism of MR in 48/68 cases classified as WHF 'borderline RHD' with isolated WHF 'pathological' MR (70.5%)., Conclusion: In a real-world, large-scale screening project, the adoption of a mechanistic evaluation based on the systematic identification of ISS-related MR markedly reduced the number of WHF 'screen-positive' cases misclassified as WHF 'borderline RHD'. Implementing strategies that reduce this misclassification could reduce the cost- and labour burden on large-scale RHD screening programmes., (© The Author(s) 2021. Published by Oxford University Press on behalf of the European Society of Cardiology.)