One to "infinite lines" isn't something filemaker can handle. That suggests you may need to restructure your database to that this isn't a problem.
One to many lines, can be handled with fields set to Slide up/shrink enclosing part (in Fmp 11 that's "resize enclosing part).
Make each field many lines tall and set the sliding/shrinking as I've described. The fields will shrink but not "grow". The effect will only be visible when you preview/pdf/print your report.
Thanks a lot
I'll use your solution, it solve my problem and the appareance of printed report is perfect.
Hospital Universitario de Salamanca