To understad the basic phenomena of blood flow in cardiovascular magnetic resonance image, ECG-gated MRI was done in 3 normal adults and an experimental study was done using flow phantom with KAIS MRI system. In three normal adults, images of descending thoracic aorta were evaluated at the same slice according to the different cardiac phases. MR signal was highest in the images at end diastole immediately and 80mses after R wave. No signal was detected in mid-systolic phase due to signal loss of the rapidly flowing blood. At the first slice of the multi-slice technique in flow phantom, the relative intensity I/Io was maximum as 2.39 at 1.8cm/sec among the 9 different velocities of the water flowing through the PVC tubing of 0.96cm diameter. As the velocity increased, the relative intensity of the MR signal decreased to ecome completely absent at 42.3cm/sec velocity. At the first slice, the shape of the transaxial image was homogeneously round in slower flow. However, it became irregular due to turbulence at 28.8cm/sec. At the 2nd slice, the shape of the image was similar with 1st ones in low velocities. As the velocity increased they changed into ring or smaller round shapes