you treat the cat with Revolution, it will be well protected all the time. If
they use the same litter boxes it is not possible to take heartworm medication.
The vector for heartworms is mosquito. The mosquito needs to bites the pets
which have heartworms and after that needs to bite other pets which then get
infected with heartworm (Dilofilaria immitis) If you live in the heartworm
region, it is indicated to have good protection for your pets. If the cat
(indoor or outdoor) is bitten by mosquitos, they may get infected with
heartworms, if the mosquito is infected and if the pets are not protected.
advice is to protect all your pets if they are at risk for heartworms. It is
best to consult your vet on this because he/she know better if the risk is low