The infectious diseases of the cardiovascular system infect the blood, blood vessels, and heart. In many cases, the infections remain in these areas, but in others, the infections are spread to secondary organs. The diseases of the lymphatic system affect the lymph, lymph vessels, lymph nodes, and lymphoid organs, such as the spleen, tonsils, and thymus. The diagnosis infective endocarditis describes infection of the endocardial surface of the heart and indicates the presence of micro-organisms in the lesion. In most cases, the heart valves are affected, but the disease can also occur on septal defects or on the mural endocardium. The disease has been classified as acute or subacute based on the progression of the untreated disease. Heart disease or cardiovascular diseases are the class of diseases that involve the heart or blood vessels. While the term technically refers to any disease that affects the cardiovascular system, it is usually used to refer to those related to arteriosclerosis. While many more pathogens will likely be identified in patients with cardiovascular diseases, certain easily cultured and readily identifiable microbes have been repeatedly identified in people with such conditions including H. pylori, cytomegalovirus, and Chlamydia pneumoniae.