•Cardioplegic solutions, particularly those with high potassium content, are essential for myocardial protection during CPB but can temporarily impair conduction if not fully cleared from the conduction tissues, particularly the atrioventricular (AV) node and His-Purkinje system (1).

•In this patient, the temporal relationship between delivery of cardioplegia and failure to regain a native rhythm suggested that residual cardioplegia may have played a role in suppressing AV nodal conduction.

•Differential diagnosis for complete heart block coming off bypass is broad (Table 1.1) and includes structural injury (e.g., iatrogenic trauma to the AV node during valve surgery), ischemia, electrolyte disturbances, hypothermia, or infarction.

•Prematurely attributing the complete heart block to a permanent cause might have led to unnecessary escalation—such as permanent pacemaker placement or prolonged cardiopulmonary bypass time with aggressive, escalating inotropic support.

•Instead, the team’s decision to allow for additional time for myocardial washout ultimately led to spontaneous recovery of AV nodal conduction, avoiding unnecessary interventions.

•In summary, this case underscores the importance of maintaining a broad differential diagnosis when conduction disturbances are observed during weaning from cardiopulmonary bypass, including the possibility of residual cardioplegia.