Background/Introduction: Cardiac sarcoidosis (CS) is frequently underdiagnosed due to its heterogeneous clinical presentation and the limitations of conventional cardiac magnetic resonance imaging (CMR). Early detection is crucial to prevent irreversible myocardial injury and optimise management. Multimodal imaging with 18F-fluorodeoxyglucose positron emission tomography–computed tomography (FDG PET-CT) can enhance diagnostic accuracy, particularly when CMR findings are inconclusive. Emerging quantitative parametric CMR techniques, such as native T1 and T2 mapping, may further improve detection as their clinical use becomes more widespread. Purpose: This study evaluates the added diagnostic value of FDG PET-CT in patients with high clinical suspicion of cardiac sarcoidosis following inconclusive CMR findings in a tertiary care setting. Methods: We retrospectively analysed 30 patients with suspected or biopsy-confirmed CS who underwent both CMR (including parametric mapping where available) and FDG PET-CT between 2014 and 2025. Diagnosis of cardiac sarcoidosis was established using a combination of clinical and imaging findings in accordance with contemporary guideline recommendations. Imaging findings, including quantitative mapping and FDG uptake patterns, as well as diagnostic timelines and subsequent management decisions, were reviewed and compared. Results: Of the 30 patients, 19 (63%) had biopsy-confirmed cardiac sarcoidosis, and 11 (37%) had histologically confirmed systemic sarcoidosis with cardiac symptoms suggestive of CS. CMR correctly identified CS in 14 patients (47%), while FDG PET-CT identified CS in the remaining 16 patients (53%). Among these 16 patients, 12 (75%) had unremarkable CMR findings, and 4 (25%) were initially misdiagnosed with dilated or non-dilated left ventricular cardiomyopathy by CMR. Conclusions: FDG PET-CT identified a considerable number of cardiac sarcoidosis cases that were not detected by CMR, highlighting the complementary value of a multimodal imaging approach. Delays in CS diagnosis may contribute to therapeutic gaps, highlighting the importance of integrating FDG PET-CT into diagnostic pathways. These findings support the use of multimodal imaging strategies and may inform future prospective studies aimed at improving sarcoidosis detection.For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text.