Cardiac magnetic resonance (CMR) is considered the gold-standard noninvasive technique for the quantification of ventricular volumes by cine-imaging and of vascular flows by velocity-encoded phase contrast (VENC). In routine CMR scans, it is common to found clinical conditions, as valve regurgitations and cardiac shunts, producing a volume overload and significant mismatch between the right and left ventricular stroke volumes (RSV and LSV). In the presence of a valve regurgitation, the volume overload involves the respective ventricular chamber, whereas in cardiac shunts, the location of the volume overload depends on the site of the anatomic defect. Moreover, when a cardiac shunt is present, pulmonary and systemic cardiac outputs are different (Qp/Qs < 1 or Qp/Qs > 1), whereas in the presence of valve regurgitation, Qp/Qs = 1. Therefore, by combining the cine-imaging with the VENC technique, it is possible to investigate the cardiac physiology underlying different pathological conditions producing volume overload, and to quantify this overload (the regurgitant volume and/or shunt volume). In this report, we discussed the technical, theoretical and methodological aspects of this sort of 'virtual catheterization' by CMR, providing a simple algorithm to make the correct diagnosis.