OBJECTIVES: Cardiac rhythm diseases related to syncope are of increasing incidence and prevalence worldwide including Colombia. Diagnosing transient arrhythmia is difficult with short term monitoring methods. We sought to compare cost-effectiveness of 24-hours Holter and up to 30 days ELR, each with different diagnostic yield, compliance, and costs in patients with syncope in Colombia. METHODS: An analytical decision tree model was constructed including diagnostic yield, patient compliance, mortality rate, QALYs, associated costs to diagnosis and not having a diagnosis. Third party payer perspective, five year horizon and 3.5% discount rate for utilities and costs were assumed. Patient pathways and model inputs were ascertained from doctor interviews and literature search. Average market prices of US$175 for 24-hours Holter and US$627 for ELR were used. Micro-costing for avoided emergency visits and hospitalizations was done via Colombian key opinion leader interviews and official tariffs for costs of not having a diagnosis along five years. Uncertainty adjustments were done when judged appropriate. Incremental Cost Effectiveness ratio (ICER) was done, incorporating deterministic and probabilistic sensitivity analyses. RESULTS: