The connective tissue diseases, which include systemic lupus erythematosus (SLE), ankylosing spondylitis (AKS), rheumatoid arthritis (RA), scleroderma, polymyositis and dermatomyositis, and mixed connective tissue disease (MCTD), are the systemic illnesses that most commonly affect the heart. These autoimmune-mediated inflammatory diseases affect predominantly the musculoskeletal system, but associated heart disease is common and an important cause of morbidity and mortality. They involve the heart valves, pericardium, and myocardium most frequently. The great vessels and conduction system (with the exception of AKS) and coronary arteries are uncommonly involved. The reported prevalence rates of heart disease in these conditions vary widely because of differences in patient characteristics, preselection bias, variability in the definition of cardiovascular abnormalities, and differences in the diagnostic methods used.