If you live in a heartworm-endemic area, yes.  Heartworm is
transmitted by mosquito, so generally areas with lots of mosquitos
have a lot of heartworm too.

Dr. Deborah W. Kemmerer, DVM, writes:

    My practice has been "ferret-intensive" for about nine years. I've
    diagnosed and treated about thirty ferrets for heartworms. Many
    who were not on preventive have been found to be heartworm-
    positive on necropsy when presented for "sudden death
    syndrome". In my opinion, any ferret in a heartworm-endemic area
    should be on preventive even if he never goes outside.

    The American Heartworm Society recommends Heartgard for use in
    ferrets.  In theory this is great, but sometimes less than
    practical. Most ferret owners are not comfortable with giving
    tablets and most ferrets will not consume the entire "brick" of
    the canine chewable monthly tablet. The new Feline Heartgard is
    promising, however. In a taste test using ferret patients
    conducted at this hospital, we observed about 60% acceptance of
    the small feline chewable tablet. This will be a relief to many
    owners who do not enjoy administering the liquid mixture described
    below.  

    If a ferret will not eat the chewable feline tablet, this is what
    I use as an alternative: Mix 0.3 cc's of Ivermectin 1% Injection
    in one ounce of propylene glycol (Ivermectin is not
    water-soluble). this makes a 100 microgram/ml
    suspension. Administer 0.1 cc per pound of body weight once
    monthly by mouth. We dispense the mixture in amber bottles with
    appropriate warnings about sunlight, and we put a two- year
    expiration date on it. The injection itself has a longer
    expiration date, so this should be adequate.

    I have been using this mixture since 1988. Owner compliance is
    very good, complications and side effects are virtually nil, and
    no ferret who is taking it has been diagnosed with heartworms. I
    do see heartworm-positive ferrets who are not taking preventive. I
    don't worry too much about the lack of USDA approval for ferrets,
    because there is virtually nothing approved for any use in ferrets
    with the exception of two vaccines anyway.

    The CITE Snap test for occult heartworms has proven to be very
    accurate and dependable for use in ferrets. It has shown positive
    results even in the face of only one or two very stunted adult
    worms. I cannot attest to personal experience with accuracy in any
    other antigen test.


Dr. Kemmerer reports that in her experience, all heartworm-positive
ferrets die without treatment.  If your ferret tests positive for
heartworm, contact Dr. Kemmerer at 352-332-4357 for information about
the regimen she recommends, which she has found to give about a 75%
survival rate.

If your pets are on heartworm preventative, consider giving it to them
all year.  That removes the possibility that a worm might sneak in
before you start it up again, so your pet will be safer, and won't
have to have another heartworm test every spring.

Just so you know, the signs of a heartworm infestation include chronic
cough, lethargy, labored breathing, fluid accumulation in the abdomen,
fainting, and a bluish color to the tongue, gums and lips.