OBJECTIVE: To validate a new index, the surface-length index (SLI) based on area change in a short-axis view and length reduction in the horizontal long-axis view, which is used to quickly (<1 min) detect right ventricles with an abnormal ejection fraction (EF) during a cardiac MRI examination. SLI can be used to avoid a complete delineation of the endocardial contours of normal right ventricles. METHODS: Sixty patients (group A) were retrospectively included to calibrate the SLI formula by optimisation of the area under the ROC curves and SLI thresholds were chosen to obtain 100 % sensitivity. Another 340 patients (group B) were prospectively recruited to test SLI's capacity to detect right ventricles (RVs) with an abnormal EF (<0.5). RESULTS: The appropriate threshold to obtain 100 % sensitivity in group A was 0.58. In group B, with the 0.58 threshold, SLI yielded a sensitivity of 100 % and specificity of 51 %. SLI would have saved 35 % of the RV studies in our population, without inducing any diagnostic error. SLI and EF correlation was good (r (2) = 0.64). CONCLUSION: SLI combines two simple RV measures, and brings significant improvement in post-processing efficiency by preselecting RVs that require a complete study.