Top dog heard (4)
I believe the answer is:
peak
'top' is the definition.
(synonyms)
'dog heard' is the wordplay.
'dog' becomes 'peke' (short for Pekingese).
'heard' indicates a 'sounds like' (homophone) clue.
'peke' is a homophone of 'PEAK'.
(Other definitions for peak that I've seen before include "Pointed mountain" , "Part of cap; mountain" , "'Heyday'" , "Sharp pointed summit" , "Acme" .)