On 23 January 1905, a small, unpopulated area of Hjartdal was transferred to the neighboring Seljord Municipality.

The old river name is likely derived from the word hjǫrtr which means "red deer".

The official blazon is "Vert, a deer at bay argent" (Norwegian: På grøn grunn ein ståande sølv hjort).

This means the arms have a green field (background) and the charge is a red deer (Cervus elaphus) standing at bay.

The deer has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used.

Counting from west to east, the villages of Åmotsdal, Svartdal, Hjartdal, Tuddal, Sauland, Gransherad, Bolkesjø, Jondalen and Lisleherad were all at one point included in the same parish.

Today, the Hjartdal parish and municipality consists of the three main village areas: Hjartdalsbygda, Sauland, and Tuddal.

The mayors (Norwegian: ordførar) of Hjartdal (incomplete list): The municipal council (Kommunestyre) of Hjartdal is made up of 17 representatives that are elected to four-year terms.

The tables below show the current and historical composition of the council by political party.