In my garden I found this vine climbing on my citrus trees. Could some expert help me identify this plant ? Is it toxic ?

Welcome to the site Carlos.
I have absolutely no knowledge of Brazilian vines but the leaves kind of vaguely (very vaguely) look morning glory-ish. Seedpod doesn't though (of those m.g. I'm familiar with).

Looks like it may be one of the Aristolochia. They have very unusual flowers. http://garden.org/plants/searc...

It reminds me of Aristolochia too: http://www.brazilplants.com/ar...

There are 5 species of Aristolochia in the state Pernambuca, N-E Brazil:

-Aristolochia birostris
-Aristolochia labiata
-Aristolochia papillaris
-Aristolochia sepicola
-Aristolochia trilobata
http://floradobrasil.jbrj.gov....

I only found one picture of the flower of Aristolochia papillaris
https://www.flickr.com/photos/...
and a botanical drawing also illustrating the seedpod:
http://www.scielo.br/img/revis...


Aristolochia labiata is also a candidate..
https://www.google.be/search?q...

Aristolochia sepicola, only found a flower photo;
https://www.flickr.com/photos/...

The other two species don't have a leaf match.

If you get a flower on your plant, it would give you a sure id.

Some info about the Aristolochia genus, like most toxic plants they also have much appreciated medicinal qualities.
https://en.wikipedia.org/wiki/...