OBJECTIVES:  The objective of this study was to compare revenue and health outcome benefits associated with two canine heartworm prevention (HWP) modalities: long-acting moxidectin (LAM) injection and oral monthly HWP. LAM is given in the veterinary clinic every 6 months, while oral monthly HWP is purchased by the pet owner from the clinic and given at home each month. METHODS:  In 2014, a retrospective 5 year (2009-2014) records analysis was conducted at 18 veterinary practices to determine the health and revenue benefits of the second LAM injection (which occurs 5-7 months after the annual wellness visit). One thousand six hundred twenty-six invoices for 918 dogs met the study review criteria. In 2016, we conducted a similar analysis at 9 of the 18 practices for dogs on oral monthly HWP. In this study, 1,177 invoices for 396 dogs met the review criteria. RESULTS:  The second LAM visit allowed the veterinarian to evaluate dog health for a second time in a single year. This resulted in identification of more health issues (22%) than those diagnosed at the annual wellness visit (10%) or the monthly HWP return visit (4%) 5-7 months later. Practice revenue was higher for the second LAM visit than for monthly HWP, with an average invoice of $121.13 for LAM compared with $56.41 for monthly HWP. Finally, the average cost of LAM ($45.96) was less than the average cost of 6 months’ worth of monthly HWP ($54.06). CONCLUSIONS:  The second LAM visit identified more health issues than the comparable return visit for dogs on monthly HWP and delivered nearly $65 more clinic revenue. Economic projections for an average veterinary clinic with 3,000 - 5,000 dogs showed that if 25% received LAM for HWP, the clinic would generate $48,750 - $81,250 additional revenue per year.