Side-effects of the experimental hormone treatments he is given to stabilize his reinvigorated and improved body cause the Russian to develop breasts (which he adores) and an implied form of menstruation, which prompts him to begin wearing women's clothing, including high heels.
The experimental hormone treatments cause the Russian man to experience physical changes that are traditionally associated with women, such as breast growth and menstruation, which in turn lead him to embrace a more feminine appearance by wearing women's clothing and high heels.