Cardiovascular disease, including heart disease, is the leading cause of death in NZ accounting for one third of deaths and in addition causing a significant burden on the health system. Ischaemic heart disease affects one in 20 adults and NZ also has exceptionally high rates of heart valve disease. Although significant resources are directed at the prevention of heart disease, surgical intervention is still required and open heart surgery remains one of the commonest forms of major surgery with 3500 adult cases each year in NZ. One in seven of these patients have a significant complication which affects patients, increases costs and reduces the resources available for surgery for others. The Improving Outcomes after Cardiothoracic Surgery Network (IOACSNet) has been established to conduct a comprehensive programme of research investigating if 5 simple and cheap interventions can reduce the number and severity of these complications resulting in better outcomes for patients.