We have shown recently that human infants with CoA show signs of derangement in their autonomic cardiovascular function in the early neonatal period (1), and this may play a role in the high incidence of hypertension in this patient group. To investigate cardiovascular autonomic dysfunction in more detail we have developed a rat model of CoA. In a preliminary operation in 1-3 day old rat pups (anaesthetized with ketamine, 60 mg kg^-1, and medetomidine, 250 μg kg^-1), the abdominal aorta was exposed via a retroperitoneal approach and isolated from the surrounding connective tissue. A ligature was placed around the aorta, either superior (SR; n=5) or inferior (IR; n=3) to the renal arteries, and tightened around a 25g needle which was then pulled free. A control group (n=7) consisted of exposing the aorta without placement of a ligature. Three to six weeks later rats were re-anaesthetized (2% halothane, reduced to 0.75% after completion of surgery) and carotid and femoral artery blood pressures (BP) were measured, as well as baroreceptor reflex gain following bolus injections of phenylephrine (0.5-2.5 μg). Data are expressed as means ± S.E.M. Statistical significance was determined using Student’s unpaired t test. Differences were considered significant at p < 0.05. Carotid BP was increased in SR CoA but not in IR CoA (129.7 ± 6.9 and 103.6 ± 3.0 v 106 ± 5.1 mmHg control, respectively). The pressure gradient across the constriction was greater in both CoA groups (21.4 ± 1.3 and 9.8 ± 0.9 v 5.2 ± 0.7 mmHg control, respectively). Baroreflex gain was reduced significantly in the SR CoA group but not the IR CoA group (0.64 ± 0.26 and 1.45 ± 0.32 v 1.51 ± 0.23 control). Post mortem examination revealed that the heart weight of the SR CoA, but not the IR CoA group was significantly heavier than control (1.3 ± 0.1 and 1.0 ± 0.1 v 1.2 ± 0.03 g control). These data show that in the rat SR CoA, but not IR CoA, causes increased BP and reduced baroreflex sensitivity, and is similar to the autonomic cardiovascular dysfunction observed in the human CoA infant. The SR CoA rat, therefore, is a suitable model for studying autonomic changes associated with CoA.