The whole family experiences stress when a child is diagnosed with heart disease. Families are currently concerned about their child's health. During this period, nurses are crucial in informing parents or other caregivers about the child's condition, the procedure, and the care provided before and after the procedure. This study aimed to evaluate the effect of instructional guidelines regarding early ambulation on knowledge, attitude, and anxiety among mothers of children with congenital heart diseases post-cardiac catheterization. Research design: A quasi-experimental research design was used to achieve the aim of this study. Setting: This study was conducted at the Department of Pediatric Cardiology at Sohag University. Subjects: A convenience sample of 50 mothers of children with congenital heart disease was enrolled in the study after cardiac catheterization. Tolls of data collection: Tool I Interviewing Questionnaire Sheet Tool (II) Nurses' Attitude toward Early Ambulation Tool (III): The state-trait anxiety inventory. Results: The results showed a positive and significant relationship between mothers' knowledge scores and their performance after one month of implementing the educational guidelines. There were highly significant improvements in mothers' knowledge and attitude regarding early ambulation post-instructional guidelines implementation (P=0. 001). Statistically significant differences and reductions were detected between anxiety mean scores after one month of implementing the instructional guidelines. Conclusion: The introduction of instructional guidelines for early ambulation improved the knowledge and attitude of mothers of children with congenital heart disease, as well as their anxiety levels. Recommendations: Instructional guidelines for mothers of children with congenital heart disease should be conducted, discussed, and integrated into rehabilitation programs.