New research from The University of Manchester indicates that heart surgeries commencing in the late morning (10:00 to 11:59) are associated with a modest, but statistically significant, 18% higher risk of cardiovascular death compared to operations performed in the early morning (07:00 to 09:59). This study, led by Dr. Gareth Kitchen, a Clinical Senior Lecturer at the University, analyzed four national datasets encompassing over 24,000 patients across England, Wales, and Northern Ireland. The findings were published in the journal Anaesthesia. The research highlighted that while the timing of surgery did not impact complication rates or hospital readmissions, the elevated mortality risk for late-morning procedures remained consistent even after accounting for surgical complexities and durations. The study posits that the body's internal clock, or circadian rhythm, may play a crucial role in influencing surgical outcomes. Dr. Kitchen emphasized that despite the statistical significance, the increased risk is relatively modest, and the majority of patients are unlikely to be affected. However, he noted that even minor improvements in timing-related outcomes could offer substantial benefits given the high volume of heart operations performed annually. This study adds to an ongoing scientific discussion, with some previous research in 2017 suggesting better outcomes for afternoon heart surgeries due to circadian clock alignment. Conversely, a 2021 meta-analysis concluded no significant effect of daytime on clinical outcomes or myocardial injury in cardiac surgery patients, and a 2007 study found no influence of circadian variation on mortality in non-emergent coronary artery bypass graft (CABG) surgery. The University of Manchester researchers suggest that integrating body clock biology into surgical planning could pave the way for a more personalized, precision medicine approach, acknowledging that individual circadian rhythms vary.