Atrioventricular (AV) nodal recovery properties can be studied by a periodic premature stimulation protocol performed at a slow basic rate. Developmental aspects of these properties have not been determined. The purpose of this study was to determine the developmental changes of AV nodal recovery properties. Forty-three children and young adults (male:female ratio 25:18) without AV nodal disease (aged 3.3 to 21.9 years) were studied by delivering premature atrial extrastimuli coupled to basic driven atrial beats. The individual recovery curve was fitted to the equation: A2H2 = A0H0 + exp(alpha -H1A2/tau) for H1A2 > or =theta, where A0H0 is the minimum AH interval, H1A2 is any recovery interval that exceeds the nodal effective refractory period, A2H2 is the corresponding nodal conduction time at any given H1A2, alpha is a constant, tau is the recovery time constant, and theta is the nodal effective refractory period. We found that: (1) A0H0 and alpha constant did not change significantly with age; (2) both tau (r = 0.324; p <0.05) and theta (r = 0.401; p <0.05) had a positive correlation with age; and (3) the maximum change in A2H2 with a 10-ms decrement in H1A2 was 32 ms and did not change significantly with age. Our results suggest that AV nodal recovery properties are age-dependent and both the recovery time constant and effective refractory period lengthen with age.