What is the burden of proving vindictiveness against a defendant in a civil case?

"Where the defendant shows that the prosecution has increased the charges in apparent response to the defendant's exercise of a procedural right, the defendant has made an initial showing of an appearance of vindictiveness. [Citation.] The defendant need not demonstrate that the prosecution in fact acted with a retaliatory motive. [Citation.] Once this prima facie case is made, the prosecution bears a 'heavy burden' of dispelling the appearance of vindictiveness as well as actual vindictiveness." ( Twiggs v. Superior Court, supra, 34 Cal.3d at p. 371, 194 Cal.Rptr. 152, 667 P.2d 1165.)