The median effective dose (ED50) and ED95 of intranasal dexmedetomidine as a single bolus have not been described for sedation in children undergoing transthoracic echocardiography (TEE) study. This information is important to compare agents and to determine the most effective sedative dose. The investigators performed a two-stage study to determine the ED50 and the ED95 of intranasal dexmedetomidine to investigate age-related differences in participants undergoing transthoracic echocardiography study.