In this paper the author examines the contradictions between Cuba and the USSR after the Cuban Missile Crisis. The author's review of the academic literature on the subject reveals that both the conflict itself and its short-term consequences have been extensively analysed. Yet, as far as one could ascertain, there is no historiography that sheds light on the further development of the contradictions between Cuba and the USSR in the 1960s. Drawing on documents from the Soviet embassy in Cuba held in the Russian State Archive of Contemporary History, the author demonstrates that the Cuban government was still extremely concerned about its security and on several occasions even attempted to join the Warsaw Pact. Contradictions between the two countries deepened with the radicalisation of Cuban position on the international stage and the implementation of guerrilla tactics pursued by Ernesto Guevara, who also tried to implement them during his trip to Africa at the turn of 1964-1965. This is evident from the notes the revolutionary took during the trip. The document, held in the personal archive of Guevara at the Che Guevara Studies Centre in Havana, is being introduced into academic discussion for the first time. The author explores the contradictions between the USSR and Cuba over issues of socialist construction, taking as an example the economic debates in Cuba and the attempt to introduce the budgetary finance system, which was later replaced by the economic register, implying the total negation of monetary relations. The study shows that Cuban socialist construction schemes in the 1960s reflected a radical political economy approach that could not be characterised as classical “real socialism”.