Psychomotor problems are common in children with congenital heart disease (CHD) but their neuropsychological basis remains unknown. This study investigated motor planning, motor control, and motor slowness, three subprocesses potentially underlying these psychomotor deficits. Using various drawing tasks, 45 school-age children with CHD were compared with 41 healthy peers on several kinematic properties. Taking longer to initiate and execute their movements than the controls, the children with CHD exhibited significant motor slowness. No evidence was found for deficits in planning or motor control. Thus, motor slowness appears to be the major determinant of psychomotor problems in school-age children with CHD.