Cryptic species within the section Fumigati, that is Aspergillus fumigatus-like species, are increasingly reported in the literature as causative agents of invasive aspergillosis (IA) in both humans and animals. Their detection and proper identification are important, but even more important is to determine the susceptibility profile (minimum inhibitory concentrations, MICs) of the isolate to antifungals using appropriate methods. Cryptic species often demonstrate elevated MICs to drugs recommended for IA therapy such as voriconazole or amphotericin B. Presented is a case of pulmonary aspergillosis in a 63-year-old male heart transplant recipient. Aspergillus lentulus with reduced susceptibility to voriconazole and amphotericin B was identified as the causative agent of the infection using culture and DNA sequencing. Susceptibility to antifungals was confirmed by the standard EUCAST-AFST methods. Based on MIC values obtained in vitro, therapy was switched from voriconazole to posaconazole with excellent clinical effects. To the best of our knowledge, this is the first reported case of A. lentulus infection treated with posaconazole and, moreover, a successful one.