heart·beat 
/ˈhɑɚtˌbi:t/ noun
plural heart·beats /ˈhɑɚtˌbi:t/ noun [count] : the action or sound of the heart as it pumps blood
▪ The patient had a rapid heartbeat. ▪ irregular heartbeats
▪ 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.
▪ Even though the job was difficult, he says he'd agree to do it again in a heartbeat.
