Ventricular septic defect is the reason i fail to gain weight? ?

Not likely: It really depends upon how severe the ventricular septal defect is. Most VSD's are very minor, meaning that almost no blood is shunted from one ventricle to the other. In those cases they do not cause any symptoms. If there is significant shunting, you might experience breathing difficulties, fluid buildup and also failure to gain. However failure to gain would never be the only symptom.

No: Ventricular septal defect, depending on the size, and location, may cause you to have cardiomegaly, and other cardiovascular symptoms, which can lead to heart failure. This usually results in fluid retention, and weight gain, and not weight loss. Etiologies of weight-loss, or fail to gain weight related to total caloric intakes, versus basal metabolic caloric consumption, which are numerous.