Preoperative investigations in cardiac surgery can be divided into diagnostic studies and assessment of fitness for surgery. Diagnostic investigations are used to detect and evaluate coronary, valvular, myocardial and thoracic aortic disease. Knowledge of an individual patient's co-morbidities helps to determine the risk of postoperative morbidity and mortality, and allows for more accurate informed consent. Furthermore, the results of preoperative investigations may predict the likely postoperative support required in order to maximize the chances of an uneventful recovery. This contribution highlights the tests for preoperative diagnosis and assessment of fitness for surgery in adult cardiac patients. In combination they guide clinicians in making appropriate management decisions, particularly with regard to elderly, frail or complex cardiac cases, discussed in the setting of joint cardiology and cardiothoracic meetings.