Recently, results of several cardiovascular clinical trials conducted in Japan were published. Most of them were designed as prospective randomized open-label blinded end-point (PROBE)-type trials, in which patients were randomly allocated to different regimens and both the patients and doctors are aware of the regimen being administered. Although the PROBE design enables performing trials resembling real-world practices, entails low costs and renders patient recruitment easier, it presents several conditions that have to be satisfied to acquire accurate results, due to its open-label nature. Principally, the so-called hard end points, which are judged by objective criteria, should be used as primary end points in order to prevent biases. In this article, a general description of various designs of clinical studies is provided, followed by a description of the PROBE design, and the precautions to be taken while conducting PROBE-designed trials by comparing trials conducted in Japan and the West.