From Old High German herza, from Proto-Germanic *hertô (“heart”), from Proto-Indo-European *ḱḗr (“heart”). Compare German Herz. Cognate with English heart.
האַרץ • (harts) n, plural האַרצן (hartsn) or הערצער (hertser), diminutive הערצל (hertsl) or הערצעלע (hertsele)
This is one of only a few Yiddish nouns that decline. In the singular, it is האַרצן (hartsn) in the dative and unchanged in the accusative.