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Background Positron emission tomography-CT (PET-CT) is widely used to diagnose cardiac sarcoidosis (CS). Emerging evidence suggests genetic arrhythmogenic cardiomyopathies (ACMs) may similarly present with episodes of myocardial inflammation resembling CS. We hypothesise a high rate of ACM diagnosis and associated pathogenic variants in patients with positive cardiac PET-CT scans referred for genetic testing. This study also seeks to delineate the role of PET-CT and anti-inflammatory therapy in ACM.Methods Patients at the UCLA Cardiovascular Genetics Clinic who underwent a cardiomyopathy gene panel were included. Genotypes were classified as genotype-positive (pathogenic or likely pathogenic variants), uncertain (variant of uncertain significance) or negative. Genes were grouped into ACM or non-ACM. PET-CT positivity was defined by cardiac fludeoxyglucose uptake without extracardiac involvement.Results Among 48 patients receiving PET-CT scans, 48% (23/48) were genotype-positive. Of 268 patients with pathogenic/likely pathogenic variants, 23 (8.6%) underwent PET-CT (11 ACM, 12 non-ACM). PET-CT positivity was observed in 27% (3/11) of ACM and 8% (1/12) of non-ACM cases. Two PET-CT-positive patients ( FLNC, MYH7) received steroids with variable outcomes.Conclusion Receiving a PET-CT scan yielded a high genetic diagnostic yield (48%) in our clinic. Randomised controlled trials of immunosuppressive responsiveness and novel therapeutics are needed to address treatment gaps for ACM.