Objective To investigate the 30-day mortality risk factors in elderly patients (≥70 years) with heart failure with reduced ejection fraction (HFrEF) after isolated coronary artery bypass grafting (CABG) and to construct a nomogram for predicting mortality risk. Methods A retrospective analysis of elderly HFrEF patients undergoing isolated CABG at Tianjin Chest Hospital from 2010 to 2024. Simple random sampling in R was used to divide the dataset into training and validation sets in a 7 : 3 ratio. The training set was further divided into survivors and non-survivors. Univariate logistic regression was performed to identify differences between groups, followed by multivariate logistic stepwise regression to select independent risk factors for death and to establish a death-risk nomogram, which underwent internal validation. The predictive value of the nomogram was assessed by plotting receiver operating characteristic (ROC) curves, calibration curves, and decision-curve analyses for both the training and validation sets. ResultsA total of 656 patients were included. The training set consisted of 458 patients (survivors 418, deaths 40); the validation set consisted of 198 patients (survivors 180, deaths 18). In the training cohort, univariate analysis showed significant differences between survivors and deaths for creatinine (Cr) level, brain natriuretic peptide (BNP), maximum Cr, intra-aortic balloon pump (IABP) use, assisted ventilation, reintubation, hyperlactatemia, low cardiac output syndrome, and renal failure (P<0.05). After multivariable logistic regression with stepwise selection, five independent risk factors were identified: intra-aortic balloon pump (IABP) use (OR=3.391, 95%CI 1.065–11.044, P=0.038), reintubation (OR=15.991, 95%CI 4.269–67.394, P<0.001), hyperlactatemia (OR=8.171, 95%CI 2.057–46.089, P=0.007), creatinine (Cr) (OR=4.330, 95%CI 0.997–6.022, P=0.024), and BNP (OR=1.603, 95%CI 1.000–2.000, P=0.010). Accordingly, a nomogram predicting mortality risk was constructed. The ROC and calibration analyses indicated good predictive value: training set AUC 0.898 (95%CI 0.831–0.966); validation set AUC 0.912 (95%CI 0.805–1.000). Calibration and decision-curve analyses showed good agreement and clinical utility. Conclusion The nomogram incorporating IABP use, reintubation, hyperlactatemia, creatinine, and BNP provides good predictive value for 30-day mortality after CABG in elderly patients with HFrEF and demonstrates potential clinical utility.