Vacuum Fluctuations, Zitterbewegung and Klein Paradox

This paper was written to young researches in Physics. We intend to briefly show that the Zitterbewegung is very difficult to be measured in real particles and that, on the other hand, the spectrum of measured masses of neutral vector mesons can be reasonably described taking into account the Klein Paradox effects. Key words: Dirac´s relativistic equation; vacuum fluctuations; vector mesons.