someone's heart is knocking

: some person : somebody

: a hollow muscular organ of vertebrate animals that by its rhythmic contraction acts as a force pump maintaining the circulation of the blood

: a structure in an invertebrate animal functionally analogous to the vertebrate heart

: breast, bosom

: love:2

: hearten

: to fix in the heart

: to strike something with a sharp blow

: to collide with something

: bustle

: a sharp blow : rap, hit

: a severe misfortune or hardship

: setback, reversal