It is a congenital defect in interventricular septum which divides the right and left ventricular chambers (high pressure chambers). In this condition blood flows from left (high pressure) ventricle to right ventricle (low pressure) causes increased blood flow in lungs , causes lung infection, breathlessness and failure to thrive. These defects should be closed as early as possible to avoid irreversible changes in lungs and endocarditis.