Post-operative pneumonia is the most common infectious complication after cardiothoracic surgery. It is associated with increased morbidity, mortality and resource utlization. This study sought to identify pre- and intra-operative risk factors associated with post-cardiac surgery acquired pneumonia. A retrospective analysis of patients who underwent cardiac surgery at Monash Health between 2008 and 2023 was performed. Four hundred and eighty-five of 7,275 patients suffered a post-operative pneumonia (6.7%). These patients were more likely to be smokers (n=298, 61.4% vs 56.5%, p=0.04), and have pre-existing medicated lung disease (n=96, 19.8% vs 13.2%, p<0.01). Patients who acquired post-operative pneumonia were more likely to have had pre-operative shock or resuscitation and undergone emergency surgery (p<0.01). Length of intubation was markedly increased 79.6+/-124.9 hours vs 21.1+/-44.0 hours (p<0.01), and longer ICU length of stay 176.0+/-244.4 vs 54.8+/-74.9 hours (p<0.01), as well as increased mortality (p<0.01). Post-operative pneumonia adds greatly to the resource utilisation and mortality. Identifying pre-operative factors along with assessment of radiological features that may allow for early treatment of those with post-operative pneumonia to attempt earlier intervention to decrease ICU length of stay and overall mortality.