que quiere decir "es que"
What does "es que" mean in the sentence "Es que tiene un corazón que no le cabe."
Why is it being used?
It's that ......
You could drop it off but it's a good way to make a connection with what you're saying now with what you have just said previously.
We do it in English too.
I really do like him. It's just that he has such bad breath! :p
In Mexico I found that some speakers would begin many a sentence with "Lo que pasa es que..." "What's going on is that..." It's a wordy but harmless way of introducing an explanation, providing a reason. As Kiwi Girl says, we do it too. "Pues" or sometimes "pos" also be used to kick-start a common.