Optical coherence tomography (OCT) is an intravascular imaging modality used in the diagnosis of coronary artery disease. The use of OCT in cardiology has started in the early 90s of the last century, mostly in intervention cardiology as a complementary imaging modality for coronary angiography and intravascular ultrasound. It uses infrared light and because of its high resolution allows a clear distinction of vessel wall layers and a detailed view of atherosclerotic plaque morphology and intravascular structures. OCT allows distinction between different types of plaques, such as fibrous plaque, calcified plaque, and thin cap fibroatheroma. It allows visualization of the whole arterial circumference, and also lesions that cannot be seen on the classic coronary angiography (plaque erosion, plaque dissection) which is very important in evaluating the cause of myocardial infarction. Also, OCT is useful in stent implantation optimization and adjusting the PCI strategy in different patients. With the help of OCT, it is possible to more precisely determine the required stent size for implantation and detect the inadequate expansion of the stent and/or stent position. After that, it is possible to optimize the result of stent implantation. Also, OCT can be used in patients after heart transplantation in the diagnosis of cardiac allograft vasculopathy, a common complication after transplantation and one of the most important causes of graft failure.