Inflammatory cardiac diseases such as myocarditis, cardiac sarcoidosis, vasculitis, and immune-mediated toxicities remain diagnostically challenging because clinically relevant questions often concern whether inflammation is active, resolving, or already caused a scar. Positron emission tomography (PET) has moved from a predominantly fluorodeoxyglucose ([¹⁸F]FDG)-based approach toward a broader molecular imaging platform that combines technical innovation with tracer diversification. This review summarizes recent advances in PET imaging of inflammatory cardiac disease, including new hardware and promising new radiotracers. Current evidence supports PET as a tool not only for diagnosis but also for treatment monitoring and risk stratification, and future progress will depend on standardization, histologic validation, and integration of advanced hardware, disease-specific tracers, and multimodality biomarkers into clinically actionable pathways.