The hypothesis that mild recurrent aortic obstruction produces subtle changes in ambulatory blood pressure was investigated by performing 24-hour monitoring on 11 postoperative coarctation patients. Patients (age 16.1 +/- 2.7 years) were compared with normal controls (age 15.7 +/- 2.5 years, n = 15). Surgery (end-to-end anastomosis) was performed at 6.0 +/- 1.0 years of age. There were no significant differences between patients and controls in terms of baseline blood pressure (right arm 123/78 +/- 4/3 mmHg versus 120/75 +/- 3/2 mmHg) or right leg systolic pressure (125 +/- 6 mmHg versus 123 +/- 4 mmHg). Of the 11 patients 8 had recoarctation by Doppler study (mean gradient 25.3 +/- 2.1 mmHg), 5 of 11 had a postexercise arm-leg pressure difference of > 30 mmHg, and 6 patients had aortic diameters at the site of surgery < 70% of the descending aortic diameter (by magnetic resonance imaging). There were no significant differences between the coarctation and control groups in terms of mean ambulatory systolic (125 +/- 3 mmHg versus 119 +/- 2 mmHg) or diastolic (69 +/- 2 mmHg versus 72 +/- 2 mmHg) pressures throughout the day. However, coarctation patients had a larger number of systolic pressures that exceeded the 95th percentile (18.2 +/- 5.6% versus 6.8 +/- 1.2%). These labile increases in systolic pressure correlated with residual coarctation (r = 0.642, p = 0.003). Ambulatory monitoring is a useful tool for detecting and monitoring subtle abnormalities of blood pressure control after coarctation repair.