Positron emission tomography (PET) is an excellent imaging technique for quantitative analysis with high-quality images. Myocardial perfusion imaging (MPI) using PET has high diagnostic accuracy and prognostic value. In addition, PET MPI can be used to quantitate regional myocardial blood flow (MBF) and myocardial flow reserve (MFR: hyperemic MBF/MBF at rest). Reduced MFR was often seen in coronary artery disease and also microvascular dysfunction with various coronary risk factors. On the other hand, such MFR reduction may be improved with various medical treatments with and without coronary interventions. PET perfusion study permits improvement in MFR under various medical treatments and/or modification of risk factors. MBF response to cold pressor test has recently been used to estimate coronary endothelial function which is considered as earlier process of atherosclerosis. Thus, MPI using PET holds a promise for wide clinical applications for risk analysis and patient management in cardiovascular diseases.