Sostenuto in E flat major, KK IVb no. 10, is a Waltz style piece of music written by Fryderyk Chopin, a Polish composer of the Romantic era. Chopin lived from 1810 to 1849, and he wrote this piece in 1840.

This is a grade 5 standard piece, and good for developing awareness of melodic shaping and placement. In the first half of the piece, the melody is in the right hand, with a chordal accompaniment in the left hand, so the right hand needs to be slightly louder so as not to drown out the melody. In the second half, the parts are reversed, so the left hand has the melody and the right hand has the accompaniment. This means that the left hand should now be the louder part. This switch from right hand melody and left hand accompaniment to vice versa needs to be done smoothly so as to maintain a continuous flow of the melody line throughout the piece. 

This piece of music benefits from subtle rubato (expressive freedom of tempo), and some pedal. There were no dynamics indicated by Chopin on the score, so dynamics are left to the player's discretion. 

​You can listen to another piece by Chopin here: Nocturne in F minor.

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