The accuracy of measurements of flow velocity determined by using cine MR phase velocity mapping--velocity-encoded cine (VEC) MR--was assessed by comparing VEC MR data with independent measurements in a flow phantom and in human subjects. Constant flow velocities generated in a phantom (range, 20-408 cm/sec) were determined correctly by VEC MR (r = .997, standard error of the estimate [SEE] = 7.9 cm/sec). Peak systolic velocities in the main pulmonary artery determined by VEC MR correlated well with the measurements obtained by using continuous-wave Doppler echocardiography (r = .91). Stroke volumes measured at the aorta by VEC MR and continuous-wave Doppler imaging also correlated well with each other (r = .80). VEC MR measurements of aortic and pulmonary flow provided left and right ventricular stroke volumes that correlated well with left ventricular stroke volumes determined by short-axis cine MR images (r = .98, SEE = 3.7 ml, and r = .95, SEE = 4.8 ml, respectively). Intra- and interobserver variabilities were small for both left and right ventricular stroke volumes as measured with VEC MR. These results indicate that VEC MR accurately and reproducibly measures aortic and pulmonary flow velocities and volumes in the physiologic range of humans, and can be used to measure right and left ventricular stroke volumes under normal flow conditions.