After completing the Kreutzer Sonata and the Eroica Symphony in 1803, Beethoven devoted most of the next two and a half years to Fidelio, his only complete opera. During those years he composed the Triple Concerto, op. 56, and three important piano sonatas – op. 53 (Waldstein), op. 54, and op. 57 (Appassionata) – but, for the time being, he wrote no chamber music. The opera was not well received, and Beethoven set it aside after revision and a second round of performances early in 1806. However, after yet further revision, it was revived to great acclaim during the Congress of Vienna in 1814.

In the meantime, Beethoven had returned to his instrumental roots and, from 1806 to 1816 a flood of distinctive compositions followed one after another: five more string quartets, three cello sonatas, three piano trios and the last of his violin sonatas, all these in addition to five new symphonies (nos. 4–8), three concertos, and the piano sonatas, songs and choral music he was also writing during the same years. Composed in the wake of Fidelio, these masterpieces could hardly have been unaffected by one of the greatest of all operas, just as they were enriched, and in many cases empowered, by the Eroica Symphony during what has traditionally, if somewhat misleadingly, come to be known as Beethoven's ‘Heroic Decade’.

Fidelio is indeed about heroism, but it is also concerned with other human attributes: love, faithfulness, tenderness, pity, hope – anger, vengeance and despair too. Many of Beethoven's loveliest compositions written during that decade are neither heroic nor ‘externalized’, but reflective and spiritual: the Violin Concerto, the Fourth Piano Concerto and the Pastoral Symphony, for example or, in his chamber music, the first three movements of the Piano Trio in E flat major, op. 70 no. 2, the Violin Sonata in G major, op. 96, and the slow movements in all three of the Razumovsky quartets, op. 59.

The primacy of song in opera and the need to focus on real characters, their situations and their emotions, rather than on abstractions, may well have contributed to the still greater emphasis on melody, the directness and lucidity of form, and the emotional intensity of Beethoven's post Fidelio instrumental music.