Cournand attended the University of Paris, Sorbonne and earned Bachelor of Arts degree in 1913 and Master of Arts degree in 1930.
He has a lot of honorary degrees from numerous universities: Honorary doctor of the University Strasbourg, 1957, Honorary doctor pf the University Lyon, 1958, Honorary doctor of the University Brussels, 1959, Honorary doctor of the University Pisa, 1960, Honorary doctor of the Columbia University, 1965, Honorary doctor of the University Brazil, 1965, Honorary doctor of the University Nancy, 1969, Honorary doctor of Science of the University Birmingham, 1961, Honorary doctor of Science of the Gustavus Adolphus College, 1963.
Cournand began his career in French Army, he was an auxiliary battalion surgeon from 1915 till 1919.
He met Richards at the university, together they collaborated in clinical lung and heart research and perfected Forssmann’s procedure, now termed cardiac catheterization, whereby a tube is passed into the heart from a vein at the elbow. With this procedure it became possible to study the functioning of the diseased human heart and to make more accurate diagnoses of the underlying anatomic defects. Cournand and Richards also used the catheter to examine the pulmonary artery, thus enabling improvement in the diagnosis of lung diseases as well.
Cournand began to be recognized for his research in the mid-1940s, when he was invited to speak at and lead various conferences.
He worked in the Bellevue Hospital as an instructor during 1930-1951 and as a professor from 1951 to 1964. Cournand retired in 1964 as emeritus professor of medicine, and devoted the years until his death to the study of the social and ethical implications of modern science.
During World War II, Cournand led a team of physicians investigating the use of cardiac catheterization on patients suffering from severe circulatory shock resulting from traumatic injury. Obtaining physiological measurements of cardiac output in these patients helped identify the cause of shock—a fall in cardiac output and return. As a result of these findings, it was determined that the best treatment for shock was a total blood transfusion rather than simply replacing plasma, which had previously been used and was found to cause anemia.
Cournand was a fellow of Royal Society Medicine, a member of National Academy of Sciences of United States of America, of l'Academie Nationale de Medecine in France, Academie Royale de Medecinede Belgique, American Physiological Society, Association American Physicians, British Cardiac Society, Swedish Society, Internal Medicine, Society Medicale Hopitaux de Paris, Academie des Sciences, as well as a foreign member of Institut de France.
During years of research, Cournand remained interested and involved in the arts. While still in Paris, he had become a follower of the modern art movement and was friends with such painters as Jacques Lipschitz and Robert Delaunay and such writers as Andre Breton.
In 1924 Cournand married Sibylle Blumer, a daughter of Jeanne Bucher, who was a prominent gallery owner in Paris. They were married until her death in 1959. In 1963 Cournand married Ruth Fabian, who died in 1973. He was married again, to Beatrice Bishop Berle, in 1975. He had four children, three daughters and an adopted son: Muriel Cournand, Marie-Eve Cournand and Marie Claire Cournand.