Positron emission tomography-magnetic resonance imaging (PET/MRI) is emerging as a novel diagnostic modality with exciting potential for a role in multiple cardiovascular applications. The combination of the high sensitivity of PET tracers with the excellent spatial resolution and tissue characterization of cardiac MRI will provide complementary information in a variety of cardiac pathologies. While initial efforts have focused on the combination of MRI and PET for assessment of coronary artery disease, cardiomyopathy, viability, and inflammation, this new technology holds enormous potential for molecular cardiovascular imaging. This article will review the development of PET/MRI, review the current research, and discuss potential future applications.