Persistent hypertension is one of the causes of sudden death which sometimes happens in patients operated on for coarctation of the aorta. Seven patients operated on for coarctation of the aorta were examined using exercise testing (Treadmill-Bruce), Echo-Doppler and NMR. Pressure gradients between the right upper and lower limbs were compared with those of normal young people and evaluated using NMR. The authors conclude that the patients operated on have resting blood pressure and pressure gradients, both resting and during exercise, greater than normal. Some patients operated on, with normal resting blood pressure and a slight gradient, can develop hypertension during exercise and a significant pressure gradient. Significant gradients during exercise are correlated to isthmic obstruction which is visible on the NMR. Follow-up after surgical repair of coarctation of the aorta cannot exclude measurement of exercise pressure gradients. This gives more physiological information compared with pressure gradients measured at rest.