Sternal wound complications following cardiac surgery, including sternal dehiscence, mediastinitis, and osteomyelitis, pose significant challenges in terms of management and patient outcomes. We present a case report highlighting the complex management of a patient who underwent open heart surgery for severe aortic valve stenosis, followed by sternal wound dehiscence and sternum osteomyelitis due to extended spectrum beta lactamase (ESBL) producing Klebsiella aerogenes. A multiple myeloma diagnosis was also suspected at the positron emission tomography (PET) scan and confirmed with bone marrow biopsy. Multidisciplinary evaluation of the case led to a comprehensive treatment plan. To control the sternal osteomyelitis, total sternectomy was performed followed by immediate reconstruction with a bone (tibia) graft from the tissue bank and fixation with the minimal hardware possible. A microsurgical latissimus dorsi free flap was required to reconstruct the soft tissue defect. After 6 weeks of antibiotic treatment with ertapenem and fosfomycin based on a culture of intraoperative material, no clinical, imaging, or laboratory signs of infection were seen. Multiple myeloma treatment was then started. At 1 year of follow up, no recurrence of infection occurred, and the reconstruction was stable and closed. Multiple myeloma is under chronic treatment with novel agent combination, with an excellent haematological response.