Heartbeat (5)
I believe the answer is:
pulse
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">heartbeat</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that heartbeat can be written as pulse)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pulse that I've seen before include "Heart-throb" , "Seed of bean or pea plant" , "Lentil, bean, seeds" , "Regular rhythm" , "often sought medically?" .)