In this paper we give a new proof of the characterization of the closed fragment of the provability logic of Heyting's Arithmetic. We also provide a characterization of the closed fragment of the provability logic of Heyting's Arithmetic plus Markov's Principle and Heyting's Arithmetic plus Primitive Recursive Markov's Principle. Key words: Provability Logic, Constructive Arithmetic MSC2000 codes: 03F30, 03F45, 03F50 Dedicated to Craig Smory