<p>The neutrophil percentage-to-albumin ratio (NPAR) has emerged as a potential prognostic biomarker in the context of cardiac surgery. This study aimed to evaluate the association between NPAR and all-cause mortality (ACM) among patients undergoing cardiac surgery, with the goal of identifying high-risk groups and informing prognostic assessments. Data were extracted from the Medical Information Mart for Intensive Care IV (MIMIC-IV, version 3.1) database. Participants were categorized into tertiles based on NPAR values. The primary outcomes were 30-day ACM and 360-day ACM following cardiac surgery. Cox proportional hazards regression and restricted cubic splines (RCS) models were utilized to assess the relationship between NPAR and mortality risk. Kaplan-Meier (K-M) survival analyses were conducted to compare survival probabilities across NPAR tertiles, and subgroup analyses were performed to examine consistency across different strata. A total of 2,101 patients were included in the analysis, of whom 70% were male. The 30-day and 360-day ACM rates were 2% and 6%, respectively. Higher NPAR levels were independently associated with increased risks of both 30-day ACM (adjusted hazard ratio [HR], 2.51; 95% confidence interval [CI] 1.01–6.24) and 360-day ACM (adjusted HR, 2.19; 95% CI 1.29–3.73). The RCS models demonstrated a positive, linear association between NPAR and mortality risk. K-M analyses demonstrated significantly lower survival probabilities in the highest NPAR tertile. Subgroup analyses showed no significant interaction effects. Elevated NPAR values were independently associated with increased risks of 30-day and 360-day ACM following cardiac surgery. These findings suggest that NPAR may be a valuable marker for identifying high-risk patients and improving postoperative risk stratification.</p>