Blasphemy, in the Bulgakovian sense, means not only denial of the authority of God, although it certainly does mean that. It also means insufficient humility in the face of the mysteries of nature. Bulgakov is not so reactionary as to believe in a divine or natural order of things which cannot be altered. He was a doctor, after all; he loved the rush of modernity and its machines. The message of A Dog’s Heart is that man must recognise the existence of limits to his powers; that there are realms, divine and natural, where he cannot tread without the danger of creating something blasphemous and unnatural - without carrying out a Satanic act.