Background <p>Postoperative atrial fibrillation (POAF) is a common complication following coronary artery bypass grafting surgery (CABG) which increases morbidity and mortality. Numerous studies have compared the effect of warm blood cardioplegia (WBC) to cold blood cardioplegia (CBC) on the occurrence of post-CABG AF, with inconclusive outcomes.</p> Methods <p>We conducted a retrospective single-centre study involving 601 patients undergoing isolated CABG operated on from 2022 to 2024 at the Essex Cardiothoracic Centre, Basildon and Thurrock University Hospitals.</p> <p>A 1-to-1 propensity score matching (PSM) analysis was then used to control selection bias and confounding, creating a matched cohort of 480 patients (240 receiving CBC and 240 receiving WBC). The primary outcome was the incidence of POAF. A multivariable conditional logistic regression model was used to identify independent predictors of POAF in the matched cohort.</p> Results <p>In the propensity-matched cohort, there was no statistically significant difference in the incidence of POAF between the CBC group (65 patients, 27%) and the WBC group (53 patients, 22%) (<i>p</i> = 0.3). After adjusting for all baseline and procedural covariates in the multivariable analysis, the type of cardioplegia was not found to be an independent predictor of POAF (odds ratio (OR) 0.81, 95% confidence interval (CI) 0.48–1.38, <i>p</i> = 0.44). Advancing age was the sole independent predictor, with each additional year increasing the odds of developing POAF by 12% (OR 1.12, 95% CI 1.03–1.22, <i>p</i> = 0.008).</p> Conclusions <p>In this propensity-matched analysis, the choice between warm and cold blood cardioplegia did not significantly influence the risk of developing postoperative atrial fibrillation. The primary driver of POAF risk in this cohort was the non-modifiable factor of advancing age.</p>