Summary The main objective of this article is to analyse the relations between the political directorates of the PVP and the FSLN in the 1960s, based on the correspondence between Manuel Mora Valverde and Carlos Fonseca Amador, in order to identify contradictions, discrepancies and overlaps between the leaders of both organisations: the first communist cut and the second a nationalist guerrilla born under the imprint of the Cuban model. In this regard, the question arises as to how the relations between the Partido Vanguardia Popular (Partido Vanguardia Popular, PVP) and the Sandinista National Liberation Front (FSLN) were during the 1960s, the two organisations being of a different nature and maintaining different political lines on the strategy to be pursued in the anti-somocist struggle. As a central hypothesis, it is argued that the establishment of relations between the two organisations was a complex process, marked by disconfidence and mutual differences, drawn from the very foundation of the FSLN towards the end of the 1960s, as both were the expression of two distinct revolutionary currents, which differed across the continent depending on the ways and strategies to combat the dictatorial regimes that dominated the region.