Measurement of blood flow in vessels leading to or arising from the heart is one of the key features of Cardiac Magnetic Resonance (CMR). With standard 2D phase contrast (PC) flow measurements, each vessel is measured separately at a predefined location. Planning and scanning can be time consuming while the patient is inside the scanner. In addition, when the scan time is long, the hemodynamics may be assessed at different physiological states. In contrast to a 2D PC acquisition 4D PC captures all the information about blood flow velocities within a 3D anatomical volume. Once this predefined volume has been acquired, the flow within the heart and vessels of interest can be measured at any desired location offline, i.e. after the patient has left the scanner. This is especially advantageous in cases where multiple 2D PC MRI scans are needed such as in congenital heart disease (CHD). In addition to standard measurements, 4D PC provides flow patterns, which might change our current understanding of pathologic flow conditions. Although there has been increasing interest in this new technique, only a few papers have proved its accuracy in adult population. The purpose of our study is to validate the accuracy of 4D PC flow method in quantification of thoracic and upper abdominal blood flow volumes in children. In this validation study, 4D PC flow method will be applied in 100 pediatric patients undergoing clinically indicated CMR with 2D PC flow measurement.