Does pet insurance cover heartworm? The treatment of an active heartworm infection is a covered illness claim on an accident-and-illness policy bought before the dog tested positive and past the illness waiting period, but the monthly heartworm preventive is routine care that a base policy does not pay, and a dog already diagnosed is pre-existing and excluded. Heartworm treatment runs roughly $500 to $1,500 depending on the dog's size and the stage of infection, per CareCredit's 2025 cost research [CareCredit: How Much Does Heartworm Treatment for Dogs Cost, 2025].
The split that decides this category is prevention versus treatment: the cheap recurring preventive is a wellness-add-on question, and the expensive one-time treatment is the insurance question.
The direct answer
Treating an established heartworm infection is an illness, so the treatment, the staging diagnostics, the injectable medication, and the associated hospitalization or monitoring, is a covered claim under the base accident-and-illness policy at the reviewed carriers, subject to the deductible, the reimbursement rate, and the annual limit, and only after the illness waiting period. The monthly heartworm preventive is the opposite case: it is routine preventive care, not reimbursed by any base policy, and recoverable only through a separate wellness add-on that pays a fixed amount toward routine items rather than a percentage of an illness bill.
That preventive-versus-treatment line is the whole answer. A policy bought on a healthy, heartworm-negative dog covers the treatment if the dog later contracts the disease; it never pays back the routine pill that would have prevented it unless a wellness plan is attached.
What heartworm treatment costs
CareCredit's 2025 cost guide places heartworm treatment for dogs at roughly $500 to $1,500, with the figure driven by the dog's body weight, since the injectable dose scales with size, and by the stage of infection, since a more advanced case needs more diagnostics, more monitoring, and sometimes hospitalization [CareCredit: How Much Does Heartworm Treatment for Dogs Cost, 2025]. A large dog with an advanced infection sits near the top of that band; a small dog caught early sits near the bottom.
On a $1,200 heartworm treatment at an 80% reimbursement rate with a $500 annual deductible, the policy returns about 80% of the $700 above the deductible, roughly $560, leaving the owner near $640 [CareCredit: How Much Does Heartworm Treatment for Dogs Cost, 2025]. On a $1,500 case under the same terms it returns about $800. On a $500 minor case the policy returns little, because the bill is at or near a typical deductible, the recurring reason small claims rarely pay.
The pre-existing line on heartworm
Heartworm is a textbook pre-existing trap because the diagnosis is a single positive test that lands on the record. Once a dog has tested positive, treatment of that infection is pre-existing and excluded on any policy bought afterward, defined site-wide by the NAIC Pet Insurance Model Act as a condition for which advice or treatment was received before the policy date or during a waiting period [NAIC: NAIC Passes Pet Insurance Model Act, 2022].
The decision
If a dog is currently heartworm-negative and on prevention, a base accident-and-illness policy covers the treatment should the disease ever break through, and the routine preventive belongs on a wellness add-on, not the insurance line; weigh the reimbursement rate, deductible, and annual limit on the base policy. For a dog already diagnosed, do not buy expecting coverage for that infection, it is pre-existing at every reviewed carrier; budget the treatment out of pocket and buy the policy for future unrelated conditions. The pre-existing mechanics apply to heartworm in full; see the pre-existing conditions page, and the preventive-medication line is detailed on the medications page. Every provider is reviewed the same way against the published methodology page, and the disclosure page explains how the affiliate relationship is handled.