Worldwide, over 300 million major operations are performed annually. Despite advances in many fields of medicine, there is still a relevant risk of death related to these operations. Depending on how sick the patient was prior to the operation and the type of the operation needed, between 1% and 10% of patients die within 30 days of an operation. Cardiac complications, including a heart attack, occurring either during or immediately after these operations seem to be important contributors to many of these deaths.Most heart attacks occurring during or immediately after an operation do not cause symptoms such as chest pain, as the patients is receiving high doses of anesthetic drugs at this time. Accordingly, these heart attacks are very often missed in clinical routine. Therefore, it is largely unknown how often these heart attacks occur and for how many of the perioperative deaths these heart attacks are responsible for.Also, it is unknown, why these heart attacks occur during or immediately after an operation and how these patients should be treated.Aims: To find out, how common cardiac complications including heart attacks are during or immediately after an operation, for how many of the perioperative deaths these heart attacks are responsible for,why these heart attacks occur, how these patients should be treated.Methodology: 3460 consecutive patients undergoing a major operation will be included into this pragmatic prospective observational multicentre study at the University Hospital Basel, the Cantonal Hospital Aarau, and other hospitals in Switzerland. The study will be conducted by an interdisciplinary team of cardiology, anaesthesiology, and surgery. Patients will receive measurements of a novel blood tests that allows the rapid detection of dying heart muscle cells, and therefore heart attacks. prior to the operation, as well as after the operation. The type and the most likely cause of these heart attacks will then by examined by experienced physicians. We will contact all patients after hospital discharge and check whether they are fine or whether a complications or even death may have occurred. We will then try to develop tools that allow a more precise assessment of the risk in the individual patient developing such a cardiac complication and/or death.Potential Significance: Our large interdisciplinary multicentre project will provide novel and unique insights on heart attacks occurring during or immediately after an operation. These insights will empower physicians and patients to make better assessment of the risk-benefit ratio of a planned operation. E.g. patients being told that a planned operation carries with it for them a high risk of developing a heart attack may ultimately decide against an operation and chose a conservative treatment option.