Dr. J. Willis Hurst, the cardiologist for Lyndon B. Johnson from the time of his first heart attack in 1955 and the principal editor of “The Heart,” a widely used textbook on cardiovascular disease, died on Oct. 1 in Atlanta. He was 90.

The cause was complications of a stroke, his son Philip W. Hurst said.

Dr. Hurst met his most famous patient in the summer of 1955, when Johnson, then the majority leader of the Senate, suffered a serious heart attack and was admitted to Bethesda Naval Hospital in Maryland, where Dr. Hurst was the cardiologist on call.

“Lyndon had turned gray; he didn’t look alive, didn’t look like he was breathing,” Lady Bird Johnson wrote in a foreword to “LBJ: To Know Him Better,” by Dr. Hurst and Dr. James C. Cain, Johnson’s personal physician. “It was a heart-stopping moment for me, and it lasted for the next six weeks, which was the routine stay then for heart attack patients. Dr. Hurst became the most important man in my life. He would either save Lyndon or not.”...