Background: Cardiovascular magnetic resonance measurements of the volumes of the right and left ventricle and of the flows in the ascending aorta and main pulmonary artery contribute to the assessment of patients with valvular regurgitation or intracardiac or extracardiac shunts. Ventricular volumes are measured by planimetry and summation of end-diastolic and end-systolic areas measured in a stack of ventricular short-axis cines. The volumes of blood flowing through planes transecting the great arteries are measured using phase contrast velocity mapping. The two approaches are essentially different and can be used either for mutual validation, or separately or in combination to quantify regurgitation and/or shunting. In the presence of shunts, the relations between the stroke volumes and arterial flows of each side of the heart vary depending on the level of shunting (for example, atrial, ventricular or ductal). Conclusion: This article aims to explain and illustrate the technical and theoretical basis for calculations using volumetric and flow measurements, providing formulae and diagrams to facilitate the interpretation of results.