The 33-year-old supermodel says she gave her famous assets the stereotypically German names in homage to her homeland.
She said: "They've been an ongoing joke for, like, 12 years. It started because I was from
"So when I began modelling I used to say, 'These are German breasts, one is called Hans and one is called Franz.' "
Mother-of-three Heidi, who is married to singer Seal, has also insisted she will never starve herself to become a size zero.
She said: "I have always been too round to do fashion shows. I don't look weird enough for them to want me for the catwalk that's fine.
"The other girls are always much taller and skinnier, so it just isn't my thing. I stick to what I'm good at and have never been prepared to starve myself to death and do crazy stuff just to be like a thin rail and fit into their clothes."
Heidi has two sons, Henry and Johan, with Seal, and a daughter, Leni, from a relationship with Renault Formula One boss Flavio Briatore.