Background: Postoperative thrombocytopenia is a frequent finding after cardiac surgery, affecting approximately 10–40% of patients. The early decline in platelet count, typically observed within the first 48–72 h, is usually explained by hemodilution, perioperative platelet consumption, and the inflammatory or mechanical impact of cardiopulmonary bypass (CPB). However, a secondary decrease occurring beyond postoperative day 5 should raise suspicion for more serious causes, the most important being heparin-induced thrombocytopenia (HIT), a rare but potentially life-threatening complication.

Objectives: This review aims to outline the characteristic patterns of postoperative thrombocytopenia in cardiac surgery, provide a practical framework for differential diagnosis, and summarize up-to-date evidence on the diagnosis and management of HIT. 

Methods: A narrative review was conducted through searches in PubMed, Scopus, and Embase up to September 2025.

 Conclusions: Recognizing platelet count trends early and applying a stepwise diagnostic approach can help distinguish benign postoperative thrombocytopenia from HIT and other critical causes. The combination of clinical assessment using the 4Ts score and appropriate confirmatory testing remains central to accurate diagnosis. Tailoring anticoagulant therapy to individual patient requirements—including surgical procedure, renal and hepatic function, and bleeding risk—is essential for reducing thrombotic events and improving postoperative outcomes.