/ˈhɑɚtˌbiːt/ noun, pl -beats [count]
: the action or sound of the heart as it pumps blood
The patient had a rapid heartbeat.
irregular heartbeats
in a heartbeat
US informal : in a very brief time : without any delay or hesitation
Even though the job was difficult, he says he'd agree to do it again in a heartbeat.
Useful english dictionary. 2012.