Pond or bog plant. Houttuynia cordata 'Chameleon'.

One of my favourite plants, I think you will find it is Houttuynia cordata 'Chameleon'. Yours looks very happy :-)

Thanks Xela.

You can grow it as a groundcover also, it's alot more drought tolerant than the labels suggest. You are going to love it either way, the more sun it gets the more red it becomes, but it's still beautiful without the red, when growing in the shade.