It starts out topically but will get into her system to take care of them

With cats it's usually easier to apply something topically rather than pill them... pilling cats isn't easy sometimes; most can't be fooled by hiding them in treats and its hard to shove a pill down their throat. So its usually easier to administer topically, but yes it is systematic and will treat them the same

On ProHeart: Isn't it funny that the list of warnings and side-effects is like a novel too!? I've been warned in school against using this... I forget what the active ingredient is, but it's used in other drugs too so be careful and READ LABELS OF ANY DRUG OR PESTICIDE YOU USE ON YOUR ANIMALS!