The usual non invasive diagnostic methods may not be able to estimate a mild residual gradient in infants treated for Coarctation of the Aorta (CA) so we tried to determine whether Pulsed Doppler (PD) may be useful in these cases. We studied 16 children (Group A) treated for CA, clinically considered as good operative results (arm to leg gradient less than or equal to 10 mmHg) and admitted for cardiac catheterization to study associated cardiac defects. Ten children with congenital heart disease different from CA were studied as a control (Group B). Percutaneous left cardiac catheterization was performed in all children with pull-back recording of the aortic pressure across aortoplasty before angiography. PD study was performed with an ATL Mark 600 and a 3 MHz transducer positioned in the suprasternal notch. The sample volume was moved into the descending aorta in order to obtain peak flow velocity (PFV) and estimate systolic gradient (DEG). Cardiac catheterization gradients (CCG) ranged from 0 to 20 mmHg (3.9 +/- 6.3 mmHg) in Group A while no gradient was recorded at the Isthmus in Group B. In Group A the frequency shift changed just below the aortoplasty; PFV and DEG ranged respectively from 1 to 2.3 m/s (1.6 +/- 0.3 m/s) and from 4 to 22 mmHg (10 +/- 4.8 mmHg). In Group B the descending aorta PFV ranged from 0.8 +/- 1.3 m/s (1 +/- 0.2 m/s). PFV in Group A was higher than in Group B (p less than 0.001). CCG were plotted against DEG; the linear regression gave a satisfactory coefficient of correlation (R = 0.93 and p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)