I need an english to latin translation of the phrase 'my heart is forever faithful.'?

I'm surprised by you all! Cor is neuter.

It's:

Cor meum semper fidele est.

You could also say:

Mihi cor semper fidele est.

(That's more: I have a forever faithful heart).

Cor meus semper fidelis est.

First 'cor', then 'meus' .

I know, 'cause I am CORneille. :-)))

But the next answer of GARIK is correct.

So it's also fidelE and not fidelIS.

You all should give him the thumbs up, like I did.

meus cor semper fidelis est

or

meus pectus semper fidelis est

i prefer the first one

Hope that helps ;)

Mei pectus pectoris est semper fidelis.

I'm not exactly sure but I think it's right.:)