In recent years, a growing number of observational studies in cardiology have been carried out following the criticism that rigid design of randomized clinical trials produces information that is not applicable to the general patient. This approach is very common in several branches of medicine, first of all oncology, but has often been considered marginal in cardiology. The recent introduction of new oral anticoagulants (NOACs) on the market, however, has seen a proliferation of "real-life" studies, drawing the attention of cardiologists to the advantages and limitations of post-marketing studies. NOACs have been approved for use on the basis of large randomized clinical trials that have clearly documented their efficacy and safety. Since they have become available, the analysis of phase IV data has been considered crucial and therefore a great amount of information on the use of NOACs in daily practice has become available. It should be considered, however, that the possibility exists that results obtained from "real-world" studies, which do not apply rigid scientific criteria, may lead to incorrect conclusions. Accordingly, it is mandatory to fully define the operational standards of observational studies. All the protagonists of post-marketing analysis (physicians, epidemiologists, pharmacologists, statisticians) should handle the data strictly in order to ensure their reliability and comparability with other studies. To this end, it is crucial that researchers follow rigorous operational protocols for phase IV studies. Briefly, any "real-life" study should be prospective and adhere to what is prespecified by the research protocol - which must illustrate the background and rationale of the study, define its primary endpoint, and detail the methods, i.e. study design, population and variables.