Abstract BACKGROUND: Cardiovascular health promotion in children has the ability to reduce the risk of atherosclerosis in both child and the community. Thus it seems reasonable to initiate healthful lifestyle training in childhood to promote improved cardiovascular health in adult life. Our aim is to test the hypothesis that a one - year, classroom – based education for the third, fourth and fifth elementary school graders could change their knowledge scores about healthy heart. METHODS: It was a randomized and interventional study in elementary schools of Shahr-e-kord / Iran in ۲۰۰۶-۲۰۰۷. A total of ۸ elementary schools, categorized by socioeconomic types and male and female setting, were selected and randomized into control or intervention groups. Subjects were ۹۲۰ third, fourth and fifth graders, aged ۹ to ۱۱ years (۵۰% boys and ۵۰% girls). Over a course of ۸ weeks, health educators and general practitioner of the elementary schools presented two hours sessions per week on heart function, nutrition, and exercise for healthy heart and living tobacco free for the intervention group. The education program was based on Heart Power! Program, an American Heart Association program. Statistical analysis tests wrere: Mann – Whitney U test and Wilcoxon matched- pairs signed rank test and Bonferroni correction for the two pair wise comparisons RESULTS: Total heart knowledge at post test was increased ۴۰% in the intervention group (P<۰.۰۱). Difference in means of total healthy heart knowledge scores between control and intervention group increased from ۱۲.۴ points in baseline to ۲۴.۶ points in post test ( total score was ۳۰). Attitude in intervention group changed from ۳۲% to ۶۳.۹% after post test (P<۰.۰۱). After general and heart examination, we found ۶۹ students who had abnormal heart sounds and finally by referred to pediatric cardiologist, for ۱۸ them heart diseases were diagnosed. CONCLUSION: It can be concluded that the classroom – based cardiovascular health promotion had a significant effect on the healthy heart knowledge. Therefore, schools provide an excellent setting for introducing comprehensive healthy heart education and promotion of cardiovascular health to the general population. Keywords: Healthy heart, Elementary school students, Children, School based education, Knowledge, Attitude, Cardiovascular diseases.