Forward flow quantification with four-dimensional (4D) flow MRI across the mitral valve (MV) and aortic valve in a 45-year-old man with moderate MV regurgitation diagnosed with echocardiography. A, B, Semiautomated valve tracking on two orthogonal long-axis cine balanced steady-state free precession images for each valve. Colors represent the in-plane velocity measured with 4D flow MRI. C, D, The 4D flow MRI through-plane velocity measurements are projected onto the valve-tracking plane (inset), and time-resolved streamlines are generated from within the contour.