Background <p>Intra-abdominal hypertension (IAH) is a life-threatening condition associated with increased morbidity and mortality in intensive care unit (ICU) patients. Autonomic nervous system dysfunction, reflected by altered heart rate variability (HRV), has shown prognostic significance in critical illness. This study aimed to evaluate the prognostic value of HRV in predicting mortality among IAH patients.</p> Methods <p>In the Medical Information Mart for Intensive Care III (MIMIC-III) database, we retrospectively identified adult ICU patients who had both intra-abdominal pressure (IAP) measurements and electrocardiogram (ECG) recordings available. According to IAP measurements, patients were divided into a normal IAP (N-IAP) group and an IAH group. Twelve HRV parameters were derived from RR intervals. A multivariable logistic regression model including both Sequential Organ Failure Assessment (SOFA) score and HRV variables was developed to predict in-hospital mortality. Model performance was evaluated using receiver operating characteristic (ROC) curves and area under the curve (AUC), and was compared with a SOFA-only model. Internal validation was performed using bootstrap resampling.</p> Results <p>Among 202 patients, HRV was significantly lower in the IAH group than in the N-IAP group. Deceased IAH patients exhibited significantly lower HRV than survivors. The combined SOFA and HRV model achieved an AUC of 0.832 for predicting in-hospital mortality, which was higher than that of the SOFA-only model (AUC = 0.801).</p> Conclusions <p>Diminished HRV is a critical prognostic marker for mortality in patients with IAH. Incorporating HRV into the SOFA-based model improves predictive performance for in-hospital mortality compared with the SOFA score alone.</p>