To understand the basic phenomena of blood flow in cardiovascular magnetic resonance image(MRI), ECG-gated MRIwas done in 3 normal adults and an experimental study was done using flow phantom with KAIS MRI system. In threenormal adults, images of descending thoracic aorta were evaluated at the same slice according to the differentcardiac phases. MR signal was highest in the images at end diastole immediately and 80mmsec after R wave. Nosignal was detected in mid-systolic phase due to signal loss of the rapidly flowing blood. At the first slice ofthe multi-slice techique in flow phantom, the relative intensity I/Io was maximum as 2.39 at 1.8cm/sec among the 9different 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 become completely absent at 42.3cm/sec velocity. At the firstslice, the shpae of the transaxial image was homogeneously round in slower flow. However, it became irregualr dueto 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.