Heart of Spain is compelling both for its shrewd formal aesthetics and as a sympathetic human document of the Spanish Civil War. It was begun by three international volunteers for the Loyalist cause in Spain: Geza Karpathi, a Hungarian still photographer; Herbert Kline, an American journalist who later became a professional filmmaker; and Canadian physician Norman Bethune, who hoped with this film to raise funds for the blood transfusion service he was operating along with his American colleague, Dr. Edward Barsky. Their heroic blood donation program becomes a symbol for the resilient civilian support for the Loyalist army. Karpathi and Kline entrusted their script and footage to a newly formed organization of left-wing filmmakers in America, Frontier Films--Paul Strand, Leo Hurwitz, and Ben Maddow among them. Heart of Spain became Frontier Films' first major success (important works ahead would include People of the Cumberland, 1938, and Native Land, 1942).