Objectives: Female sex is considered a risk factor for mortality and morbidity following cardiac surgery. This study is the first to review the UK adult cardiac surgery national database to compare outcomes following surgical coronary revascularisation and valvular procedures between females and males. Methods: Using data from National Adult Cardiac Surgery Audit (NACSA), we identified all elective and urgent, isolated coronary artery by-pass grafting (CABG), aortic valve replacement (AVR) and mitral valve replacement/repair (MVR) procedures from 2010-2018. We compared baseline data, operative data and outcomes of mortality, stroke, renal failure, deep sternal wound infection, return to theatre for bleeding and length of hospital stay. Multivariable mixed-effect logistical/linear regression models were used to assess relationships between sex and outcomes, adjusting for baseline characteristics. Results: Females, compared to males, had greater odds of experiencing 30-day mortality (CABG OR 1.76, CI 1.47-2.09, p<0.001; AVR OR 1.59, CI 1.27-1.99, p<0.001; MVR OR 1.37, CI 1.09-1.71, p=0.006). After CABG, females also had higher rates of post-operative dialysis (OR 1.31, CI 1.12-1.52, p<0.001), deep sternal wound infections (OR 1.43, CI 1.11-1.83, p=0.005) and longer length of hospital stay (Beta 1.2, CI 1.0-1.4, p<0.001) compared to males. Female sex was protective against returning to theatre for post-operative bleeding following CABG (OR 0.76, CI 0.65-0.87, p<0.001) and AVR (OR 0.72, CI 0.61-0.84, p<0.001). Conclusion: Females in the UK have an increased risk of short-term mortality after cardiac surgery compared to males. This highlights the need to focus on the understanding of the causes behind these disparities and implementation of strategies to improve outcomes in females.