Poor weight gain in children can be due to lungs or liver causes etc but heart diseases can also leads to poor gain in weight in children.
Poor weight gain in children due to heart diseases can be congenital defect in heart (means heart diseases that are present at birth) or can be due to acquired heart diseases.
Congenital heart diseases that can lead to this problem can be Large AP window, VSD, PDA, AVSD TGA with VSD, Truncus etc.
In these diseases, lungs of the child receives an excess of blood supply that leads to difficult feeding and breathing with loss of excess calories as compared to gain in calories, leading to loss of weight.
Acquired heart diseases that can lead to this situation can be dilatation of heart (dilated cardiomyopathy) with poor weight gain.
So, family needs to consider heart diseases also when the child is not gaining proper weight and timely and adequate treatment is necessary for adequate outcome.
Kindly refer to common cardiac condition section of www.childrenheartcare.com for detailed information of congenital heart diseases.