Tehran University of Medical Sciences Journal of Pharmaceutical Care 2322-4630 13 4 2025 12 31 318 321 Mehrshad Ebrahimpour Mashhad University of Medical Sciences Samin Ghorbani Moghaddam Mashhad University of Medical Sciences Hossein Rahimi Mashhad University of Medical Sciences Amir Hooshang Mohammadpour Mashhad University of Medical Sciences Omid Arasteh Department of Clinical pharmacy, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran 2025 06 29 2026 04 22 Carfilzomib, a proteasome inhibitor used to treat relapsed multiple myeloma, is linked to rare cardiac complications. Complete heart block (CHB), though seldom reported, poses critical risks in patients with multiple comorbidities. This case report illustrates the development of CHB in a patient with multiple myeloma and high cardiovascular risk, underscoring the importance of risk-based monitoring rather than proposing a new mechanism. A 58-year-old Iranian woman with relapsed multiple myeloma, acute coronary syndrome, hypertension, dyslipidemia, type 2 diabetes, and hemodialysis-dependent chronic kidney disease (CKD) developed CHB 48 hours after carfilzomib initiation. The Naranjo Adverse Drug Reaction Probability Scale yielded a score of 3 (indicating a “possible” adverse drug reaction). Discontinuation of carfilzomib and temporary pacemaker implantation restored hemodynamic stability. Although the patient’s hemodynamics improved following pacing, she ultimately died due to septic complications unrelated to the arrhythmia. This case demonstrates the complexity of attributing CHB to carfilzomib in a multimorbid patient. It highlights the necessity of comprehensive cardiac evaluation and risk stratification in patients receiving proteasome inhibitors, especially those with concurrent CKD, coronary artery disease (CAD), and polypharmacy. https://jpc.tums.ac.ir/index.php/jpc/article/view/869 https://jpc.tums.ac.ir/index.php/jpc/article/download/869/442