Few data exist which address the significance of the Doppler gradient across a residual narrowing in older children who have had a coarctation repaired. Therefore, we evaluated 11 patients with repaired aortic coarctation with and without residual obstruction by Doppler echocardiography. The Doppler-derived transcoarctation pressure gradient correlated poorly with catheter-measured peak-to-peak and catheter maximal instantaneous gradients when only the maximal velocity across the repair was utilized in the simplified Bernoulli equation, [r = 0.73, standard of error of the estimate (SEE) = 5.0 mmHg and r = 0.56, SEE = 7.6 mmHg, respectively]. However, when the precoarctation velocity was included in the simplified Bernoulli equation, the correlation between Doppler-derived and catheter-measured gradients became excellent. The maximal Doppler gradient correlated well with catheter peak-to-peak gradient (r = 0.95, SEE = 2.2 mmHg) and catheter maximal instantaneous gradient (r = 0.94, SEE = 3.2 mmHg). However, the maximal Doppler gradient slightly overestimated the catheter peak-to-peak gradient and underestimated the catheter maximal instantaneous gradient. The Doppler mean gradient showed excellent correlation with the catheter mean gradient (r = 0.97, SEE = 0.85 mmHg). Precoarctation velocities were generally twofold greater than published normals due to a spatial acceleration phenomenon. All subjects had residual hypoplasia of the transverse aorta such that its transverse diameter was 29% less than, and its cross-sectional area was 50% less than, the ascending and descending aorta.(ABSTRACT TRUNCATED AT 250 WORDS)