Purpose <p>Cardiac MRI 4D flow imaging represents an innovative visualization tool. This study investigated the potential of 4D flow MRI to improve preoperative planning for the surgical correction or catheter interventions of complex congenital heart anomalies, and also identify findings not easily visualized on transthoracic echocardiography in patients with poor acoustic windows.</p> Material and Methods <p>CMR imaging, including 4D flow analysis, was performed as part of the patients’ routine follow-up evaluations. The obtained CMR data was subsequently assessed by an experienced cardiac radiologist. Flow analysis enable to find previously unknown findings, resolve complex haemodynics patterns which helped plan future clinical management of patients. Flow analysis enabled the identification of previously unknown findings and resolution of complex hemodynamic patterns, guiding future clinical management of patients.</p> Results <p>We have adopted a 4-dimensional flow imaging sequence to investigate 5 distinct clinical scenarios: a Gerbode defect in preparation for surgical correction, an abnormally hour-glass shaped left atrium with dilation of the right pulmonary veins, a Fontan patient with right lung hypoperfusion and a baffle leak, a native interrupted aortic arch and pulmonary hypertension in an adult, and D-transposition of the great arteries following Mustard repair in a patient experiecing recurrent hemoptysis. 4D flow provided a comprehensive understanding of the complex anatomical associations, complex haemodynamics, and enhanced visualization of hidden findings, especially in adult patients with poor acoustic windows on transthoracic echocardiography.</p> Conclusions <p>4D flow sequence represents a promising technique for preoperative planning and 3-dimensional visualization in patients with complex congenital cardiac abnormalities.</p>