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 for a medium-sized dog averages $1,200 to $1,800, with the cost varying by the severity of the infection, per CareCredit [CareCredit: A Dog Owner's Guide to Heartworm Treatment, 2026-09].
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 puts the average cost of heartworm treatment for a medium-sized dog at $1,200 to $1,800, with the figure varying by the severity of the infection, the dog's health history, the treatment protocol, and location [CareCredit: A Dog Owner's Guide to Heartworm Treatment, 2026-09].
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 [ASPCA Pet Health Insurance: How Does Pet Insurance Work?, 2026-09]. On a $1,500 case under the same terms it returns about $800.
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, 2022-08].
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.