Background <p>Assessment of the right ventricle (RV) using cardiac magnetic resonance (CMR) imaging is essential in children after tetralogy of Fallot (TOF) repair for the early detection of complications. We aimed to evaluate the effectiveness of transthoracic echocardiography (TTE) in assessing RV volume in post-TOF repair children.</p> Methods <p>A cross-sectional study was conducted on 36 post-TOF repair children. All participants underwent history taking and clinical examination. TTE was used to assess the RV end-diastolic volume index (RVEDVI), RV end-systolic volume index (RVESVI), RV ejection fraction (RVEF), and pulmonary regurgitation index (PRI). TTE results were compared to those of CMR imaging.</p> Results <p>Participants had a mean age of 10.1 ± 3.7 years and a male-to-female ratio of 2.3:1. The echocardiographic right ventricle’s end-diastolic volume (RVEDV) (146.5 ± 44.8 vs. 144.8 ± 45.1; <i>P</i>: 0.9), end-systolic volume (RVESV) (71.1 ± 24.8 vs. 63.3 ± 26.2; <i>P</i>: 0.2), RVEDVI (137.7 ± 29.9 vs. 138.6 ± 28.9; <i>P</i>: 0.9), and RVESVI (67 ± 17.9 vs. 58.8 ± 18.3; <i>P</i>: 0.1) were comparable to CMR’s, while the RVEF was significantly lower than CMR’s (51.5 ± 6.8 vs. 56.7 ± 8.8, <i>P</i>: 0.01). The RVESVI (<i>r</i>: 0.8; <i>P</i>: 0.000), RVEDVI (<i>r</i> = 0.9; <i>P</i> = 0.000), and RVEF (<i>r</i> = 0.5; <i>P</i> = 0.001) correlated positively between echocardiographic and CMR imaging. Kappa agreement testing showed a significant association between echocardiographic measurements and those of CMR. Three equations were successfully postulated based on a linear regression model to predict CMR parameters in comparable post-TOF repair children, i.e., RVEDVI, RVESVI, and PRF.</p> Conclusion <p>Conventional echocardiography effectively assessed RV functions and volumes and can predict the indications for CMR in post-TOF repair children.</p>