The document discusses the use of chest x-rays in cardiology. It introduces the cardio-thoracic index and examines cardiac contours such as the aorta and signs of mitral stenosis. The lungs are also analyzed, including potential causes of abnormalities and what pulmonary edema and Kerley B lines indicate. Common features that can be observed on a normal chest x-ray such as the ribs and pulmonary veins are also mentioned.