As age is a determinant of cardiac refractory periods, this communication describes changes of refractory periods in an age continuum of infants, children and adults, 7 months through 77 years. Seventy patients with evidence of normal A-V conduction on scalar electrocardiogram were included. The patients were divided into six age groups: less than 2 years, 3-5 years, 6-10 years, 11-15 years, 16-30 years, and greater than 30 years. Extrastimulus technique was used to determine refractory periods in sinus rhythm or at longest cycle length assuring atrial capture, then at shorter cycle lengths. Cycle lengths (CL) for each age group were divided into ranges: CL1, 1,000-600 msec; CL2, 599-460 msec; CL3, less than 459 msec. Refractory periods at the three CL's within each age group were determined. Full recovery times of the A-V node within groups of children were determined. Statistical significance of the data was found by analysis of variance. The younger group tended to have shorter values than the older groups (F less than 0.05-0.001).