The development of sustained visual attention was examined in infants cross-sectionally at 14, 20, and 26 weeks of age. Heart rate, heart rate variability, and respiratory sinus arrhythmia were measured in a 5-min baseline period. Two methods for measuring visual attention were used. The “infant control” method consisted of checkerboard presentations which were terminated when the infant looked away from them. The “interrupted stimulus” method consisted of a blinking panel in addition to the checkerboard patterns in order to attempt to actively terminate the fixation. The visual and cardiac responses during the interrupted stimulus method were more highly correlated with baseline respiratory sinus arrhythmia than were the responses during the infant control trials. The long latency heart rate responses during the interrupted stimulus trials showed a developmental change toward more mature response patterns from 14 to 26 weeks of age. It may be concluded that: 1) sustained attention, measured with the interrupted stimulus method, increases from 14 to 26 weeks of age; and 2) baseline respiratory sinus arrhythmia is correlated with sustained attention responses and their development.