How can i change it to, for example, heart form?
A heart shaped iris is not an option. What you see in the UI is what you get.
You can't. AE's camera and Lens blur simulate a real camera. If you want something else you have to buy a commercial plug-in that allows custom shapes.
Mylenium
what plug-in is it? do you know?
GenArts' Sapphire has a custom Blur filter and I'm sure there's one In Boris Continuum as well.
Mylenium