Carbapenem-resistant Acinetobacter baumannii (CRAB) poses a significant threat in cardiac surgical units due to its ability to survive on surfaces, intrinsic multidrug resistance, and association with high morbidity and mortality. Between June 15 and June 30, 2025, a tertiary cardiac care center in Karachi, Pakistan, identified an unusual cluster of CRAB infections among post-operative cardiac surgery patients, prompting a systematic outbreak investigation. A multidisciplinary outbreak response team conducted an investigation on July 1 and July 2, 2025. Cases were defined as patients developing laboratory-confirmed CRAB infections with onset ≥48 h after hospital admission and within 30 days of cardiac surgery. Active case finding included medical record review and surveillance cultures. Direct observations assessed hand hygiene compliance, personal protective equipment (PPE) use, and environmental cleaning using standardized checklists. Environmental surveillance cultures were obtained from high-touch surfaces in operating rooms (ORs) and intensive care units. Fingerprint cultures from 10 healthcare workers (five from each setting) were screened for CRAB colonization. Seven patients developed CRAB infections: four ventilator-associated pneumonias (VAPs), two central line-associated bloodstream infections (CLABSIs), and one surgical site infection. The median age was 67 years (range 58–74), and the male-to-female ratio was 6:1. Four patients (57.1%) died, of whom two had VAP and two had CLABSI. All isolates demonstrated identical resistance profiles, including resistance to carbapenems, β-lactams, fluoroquinolones, aminoglycosides, and trimethoprim–sulfamethoxazole, with susceptibility to tigecycline and minocycline. Environmental cultures were negative. Fingerprint cultures identified CRAB colonization on one OR technician’s hands, with a susceptibility profile matching patient isolates. Observational audits revealed suboptimal hand hygiene, inadequate environmental cleaning between procedures, and inadequate compliance with PPE protocols. Our investigation revealed healthcare worker hand colonization and lapses in infection control practices as the primary drivers of CRAB transmission and underscored the critical need for sustained, resource-appropriate infection control interventions and continuous vigilance to prevent multidrug-resistant organism outbreaks in similar healthcare environments.