BACKGROUND: Decreases in heart rate variability (HRV) have been repeatedly demonstrated to be an index of effort allocation to attention-demanding tasks. Children with autistic-type problems in social interaction and in adapting to unfamiliar situations (DSM-IV: PDD-NOS) have been shown to have specific attention deficits. These children were hypothesized to exhibit less cardiac adaptivity to attention-demanding tasks. METHODS: Two groups of 18 children with PDD-NOS, judged to be hyperactive and nonhyperactive, were compared to 18 healthy children with respect to their performances on a visual attention task and the differences in HRV measured during periods of task performance and periods of rest. RESULTS: Compared to the control group, both clinical groups were found to have a stronger capacity limitation in processing high loads of information, and to be less capable of maintaining a stable task performance throughout the whole task. Both clinical groups showed significantly less decreases in HRV during the periods of task performance. The magnitude of rest-task differences in HRV was found to correlate significantly with a behavioral measure of resistance to unexpected changes in daily routines. CONCLUSIONS: Children with PDD-NOS are significantly less flexible in their autonomic adaptation to attention-demanding tasks. The findings are interpreted as reflecting a deficiency in the functional organization of those neural pathways that provide cortical control of the visceral efferents.