Introduction <p>Opioid agonist treatment (OAT) is an evidence-based intervention that reduces harms associated with heroin use. Ambulance services often serve as the first point of contact for people experiencing these acute harms. OAT access relies on dosing points and prescribers, which may be unevenly distributed geographically. This study examines the geographical distribution of heroin-related ambulance attendances across Victoria and assesses whether the presence, availability, and number of OAT service providers are associated with these harms.</p> Method <p>We merged 2023/24 Victorian heroin-related ambulance attendance from the National Ambulance Surveillance System with Victorian OAT service availability data from a statewide helpline. Three negative binomial regression models tested associations between OAT availability and heroin-related ambulance attendances at the local government area (LGA) level.</p> Results <p>Fourteen LGAs had higher than average, population-adjusted, heroin-related ambulance attendances. In Model 2, LGAs with more pharmacies offering OAT vacancies than those without had a 50% lower risk of heroin-related harms (IRR = 0.52, <i>p</i> = 0.014). Model 3 found that every 10% increase in the proportion of OAT doctors with current availability was associated with a 9% reduction in heroin harms (IRR = 0.91, <i>p</i> = 0.04). A similar trend was observed for pharmacists (IRR = 0.90, <i>p</i> = 0.08). All models found heroin harms to be approximately 70% lower in regional versus metropolitan LGAs.</p> Discussion and conclusions <p>The availability and geographic distribution of OAT providers—especially those with current capacity—are linked to reduced heroin-related ambulance attendances. Strategic placement and resourcing of OAT services could better align with population need and target hotspots. The metropolitan-regional differences warrant further investigation.</p>