The investigators performed a two-stage study to determine the ED50 and the ED95 of intranasal dexmedetomidine in children undergoing transthoracic echocardiography study. In phase 1, 120 participants were randomized in a Dixon-Massey study to describe the minimum local sedative dose. In phase 2, a further 160 participants were randomly allocated to receive sedation with doses in the upper dose-response range to define the ED95