Study was performed to assess if the increase of age can affect heart rate (HR) and systolic time intervals (STI) in a population of children, adolescents and young adults. We made polygraphic recordings in 66 normal subjects (5-25 years old) and regression equations were obtained for STI and age, HR and age and STI and HR. We found a significant relationship of HR and STI with age. Equally STI were correlated with HR. PEP/LVET ratio was unaffected by age or HR. We considered moreover mean values of HR and STI in four age-groups (5-10, 11-15, 16-20, 21-25). Data comparison showed higher LVET and lower HR in elder subjects. These had moreover higher PEP versus younger groups. The Authors believe that the relationship of HR, STI and age, undemonstrated by several other studies, can be found if we consider a large of age. Because other authors studied a little range of age, our demonstration of no statistically significant different values of HR and STI between 5-10 and 11-15 groups, authorize us to consider that the effect of age is highly significative on HR and STI among children, adolescents and young adults.