This little charmer was growing in a pond full of algae, a breeding spot for tadpoles, Dragon-and Damselflies larvae, probably for mosquitoes too! , by the side of the river.

The flowers remind me of an orchid..

Some type of Mud Plantain, possibly Heteranthera reniformis.

Heteranthera reniformis it is, Jay!
At first I thought that the leaves are a perfect match but not the flowers, nearly all pictures on the web show them with entirely white flowers until I came upon a picture with the same coloration in the heart.
https://gobotany.newenglandwil...

Heteranthera reniformis does occur in the area I found it, there's one more species mentioned in the Flora do Brasil; Heteranthera zosterifolia, which has narrow leaves.

I had trouble getting an exact match on the flower also, which is why I said possibly. There is supposed to be Heteranthera limosa growing in my area, but I haven't found any yet.