Positron emission tomography provides unique qualitative and quantitative information on myocardial perfusion, metabolism and membrane function which potentially has an important impact on diagnostic workup and treatment in patients with known or suspected coronary artery disease (CAD). CAD contributes up to one third of all deaths among persons between the ages of 35 to 60 in western countries. Risk factors and symptoms turned out to have low specificity to identify persons with the disease and thus, will not help to establish objective diagnostic workup. Assessing severity of CAD by coronary angiography and means of binary classification (disease yes/no) of morphological abnormalities, i.e. stenosis > 50%, has shown to poorly correlate with coronary blood flow and, thus, might not serve as an optimal reference standard for the disease. Cardiac PET using N-13 ammonia and Rb-82 represents a well validated and clinically usable technique for both quantitative and qualitative (semiquantitative) assessment of myocardial blood flow. However, the clinical benefit of absolute flow values for diagnosis and localisation of CAD remains controversial. Most centers rely on qualitative image interpretation due to the technical requirements for image processing needed for determination of absolute flow values. However, quantitative assessment of myocardial blood flow might offer advantages when measurement of coronary flow reserve in response to medical or interventional therapy is necessary and in addition may provide early detection of CAD in asymptomatic patients who have risk factors.