Background: The cardiovascular and respiratory systems function as a single unit and alteration in cardiorespiratory interactions, can cause significant changes in cardiac function. The aim of this study was to assess the effect of acute lower respiratory tract infection on cardiovascular system in children below 5 years of age. Methods: The present study is a case-control study conducted in respiratory, and cardiology units in pediatric department in Zagazig University hospital, during the period from January 2017 to the end of November 2017. The study included (80) children, their ages ranged between 2 months – 5 years, they divided into 2 groups; patients group included 40 patients who admitted in chest unit with clinical and radiological evidence of acute lower respiratory tract infection, selected randomly by average of 3 cases every week and control group included 40 apparently healthy children, selected from a relatives of our patients and properly matched with study group in term of age, sex, and exclusion criteria. Results: Troponin I and CK-MB in patients of bronchiolitis group was higher than its value in other patient and control groups. There was a statistically significant positive correlation of cardiac troponin I with respiratory rate and Right Ventricular Systolic Pressure in bronchiolitis group. Conclusion: Major cardiac complications occur in a substantial proportion of children with acute lower respiratory tract infection. Physicians and patients need to appreciate the significance of this association for timely recognition and management of these events.