Hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) is an emerging imaging modality that combines metabolic and anatomical data in a single session, offering promising diagnostic performance in various cardiac conditions. However, its role in inflammatory cardiac diseases (ICDs), such as myopericarditis and endocarditis, remains underexplored. This study aims to evaluate the diagnostic value of PET/MRI in ICDs through a systematic review of the literature, complemented by our institutional experience. We conducted a systematic review of PubMed, Scopus, and Embase up to April 2025, using keywords including "PET/MRI," "PET/MR", "myocarditis", "endocarditis", "pericarditis", "inflammatory heart disease", and "inflammatory cardiac disease". Studies reporting the use of hybrid PET/MRI in ICDs were included and analyzed. Additionally, we retrospectively reviewed clinical and imaging data from 33 consecutive patients who underwent PET/MRI in our center for suspected myopericarditis or endocarditis between September 2022 and March 2025. The systematic review identified 12 eligible studies evaluating PET/MRI in ICDs, highlighting its added value in cases with inconclusive findings on standalone MRI or PET. Common advantages reported included improved localization of active inflammation, better characterization of tissue damage, and enhanced diagnostic confidence. In our cohort, hybrid PET/MRI was considered diagnostically useful in 16/21 (76%) of myopericarditis cases and 9/12 (75%) of endocarditis cases, particularly for reclassifying uncertain findings and guiding clinical management. The combined analysis of the current literature and real-world clinical experience supports the diagnostic utility of hybrid PET/MRI in the evaluation of ICDs. This multimodal approach improves the interpretation of equivocal cases, facilitates accurate diagnosis, and may influence therapeutic decisions. However, larger prospective studies are needed to confirm these findings and establish standardized protocols.