medical specialty dealing with the diagnosis and treatment of diseases and abnormalities involving the heart and blood vessels (blood vessel). Cardiology is a medical, not surgical, discipline. Cardiologists provide the continuing care of patients with cardiovascular disease, performing basic studies of heart function and supervising all aspects of therapy, including the administration of drugs to modify heart functions.

The foundation of the field of cardiology was laid in 1628, when English physician William Harvey (Harvey, William) published his observations on the anatomy and physiology of the heart and circulation. From that period, knowledge grew steadily as physicians relied on scientific observation, rejecting the prejudices and superstitions of previous eras, and conducted fastidious and keen studies of the physiology, anatomy, and pathology of the heart and blood vessels. During the 18th and 19th centuries physicians acquired a deeper understanding of the vagaries of pulse and blood pressure, of heart sounds and heart murmurs (through the practice of auscultation, aided by the invention of the stethoscope by French physician René Laënnec (Laënnec, René-Théophile-Hyacinthe)), of respiration and exchange of blood gases in the lungs, of heart muscle structure and function, of congenital heart defects, of electrical activity in the heart muscle, and of irregular heart rhythms (arrhythmias (arrhythmia)). Dozens of clinical observations conducted in those centuries live on today in the vernacular of cardiology—for example, Adams-Stokes syndrome, a type of heart block named for Irish physicians Robert Adams (Adams, Robert) and William Stokes (Stokes, William); Austin Flint (Flint, Austin) murmur, named for the American physician who discovered the disorder; and tetralogy of Fallot (Fallot, tetralogy of), a combination of congenital heart defects named for French physician Étienne-Louis-Arthur Fallot.

Much of the progress in cardiology during the 20th century was made possible by improved diagnostic tools. electrocardiography, the measurement of electrical activity in the heart, evolved from research by Dutch physiologist Willem Einthoven (Einthoven, Willem) in 1903, and radiological evaluation of the heart grew out of German physicist Wilhelm Conrad Röntgen (Röntgen, Wilhelm Conrad)'s experiments with X-rays in 1895. echocardiography, the generation of images of the heart by directing ultrasound waves through the chest wall, was introduced in the early 1950s. cardiac catheterization, invented in 1929 by German surgeon Werner Forssmann (Forssmann, Werner) and refined soon after by American physiologists André Cournand (Cournand, André F.) and Dickinson Richards (Richards, Dickinson Woodruff), opened the way for measuring pressure inside the heart, studying normal and abnormal electrical activity, and directly visualizing the heart chambers and blood vessels ( angiography). Today the discipline of nuclear cardiology provides a means of measuring blood flow and contraction in heart muscle through the use of radioisotopes.

As diagnostic capabilities have grown, so have treatment options. Drugs have been developed by the pharmaceutical industry to treat heart failure, angina pectoris, coronary heart disease, hypertension (high blood pressure), arrhythmia, and infections such as endocarditis. In parallel with advances in cardiac catheterization and angiography, surgeons developed techniques for allowing the blood circulation to bypass the heart through heart-lung machines, thereby permitting surgical correction of all manner of acquired and congenital heart diseases. Other advances in cardiology include electrocardiographic monitors, pacemakers (pacemaker) and defibrillators for detecting and treating arrhythmias, radio-frequency ablation of certain abnormal rhythms, and balloon angioplasty and other nonsurgical treatments of blood vessel obstruction. It is expected that discoveries in genetics and molecular biology will further aid cardiologists in their understanding of cardiovascular disease.