heartbeat
n. countable B1 Intermediate US //ˈhɑɹtˌbit// UK //hˈɑːtbiːt// heart·beat
n. the regular sound or movement of your heart as it pumps blood. It can also mean a very short amount of time.
n. the pulsation of the heart, including one complete contraction and relaxation of the cardiac muscle. In metaphorical contexts, it refers to a very brief interval or the central driving force of an organization.
The doctor listened to her steady heartbeat.
The athlete monitored his heartbeat during the race to ensure he stayed within his target zone.
The rhythmic heartbeat of the city is most audible in the early morning when the first delivery trucks begin their rounds through the quiet streets.
From heart + beat.
Usage
Often used in the phrase 'in a heartbeat' to mean immediately or without hesitation.