BACKGROUND: Although most countries face increasing population levels of obesity and diabetes their effect on coronary heart disease (CHD) mortality has not been often studied in small island developing states (SIDs) where obesity rates are among the highest in the world. We estimated the relative contributions of treatments and cardiovascular risk factors to the decline in CHD mortality from 1990 to 2012 in the Caribbean island, Barbados. METHODS: We used the IMPACT CHD mortality model to estimate the effect of increased coverage of effective medical/surgical treatments and changes in major CHD risk factors on mortality trends in 2012 compared with 1990. We calculated deaths prevented or postponed (DPPs) for each model risk factor and treatment group. We obtained data from WHO Mortality database, population denominators from the Barbados Statistical Service stratified by 10-year age group (ages 25-34 up to 85 plus), population-based risk factor surveys, Global Burden of Disease and Barbados' national myocardial infarction registry. Monte Carlo probabilistic sensitivity analysis was performed. RESULTS: In 1990 the age-standardized CHD mortality rate was 109.5 per 100,000 falling to 55.3 in 2012. Implementation of effective treatment accounted for 56% DPPs (95% (Uncertainty Interval (UI) 46%, 68%), mostly due to the introduction of treatments immediately after acute myocardial infarction (AMI) (14%) and unstable angina (14%). Overall, risk factors contributed 19% DPPs (95% UI 6% to 34%) mostly attributed to decline in cholesterol (18% DPPs, 95% UI 12%, 26%). Adverse trends in diabetes: 14% additional deaths(ADs) 95% UI 8% to 21% ADs) and BMI (2% ADs 95%UI 0 to 5% ADs) limited potential for risk factor gains. CONCLUSIONS: Given the significant negative impact of obesity/diabetes on mortality in this analysis, research that explores factors affecting implementation of evidenced-based preventive strategies is needed. The fact that most of the decline in CHD mortality in Barbados was due to treatment provides an example for SIDs about the advantages of universal access to care and treatment.