Schedule has first couple returning on American vessel (5)
I believe the answer is:
aorta
'returning on american vessel' is the definition.
'aorta' can be an answer for 'vessel' (blood vessel). I am not certain of the 'returning on american' bit.
'schedule has first couple' is the wordplay.
'first couple' means two substitutions for 'first'.
'schedule' becomes 'ort' (I can't justify this - if you can you should give a lot more credence to this answer).
'has' says to put letters next to each other.
'first' becomes 'a' (first letter of the alphabet).
'first' becomes 'a' (first letter of the alphabet).
'ort' after 'a' is 'aort'.
'aort'+'a'='AORTA'
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "Main artery from heart" , "Major artery of the body" , "main arterial route" , "Major blood vessel" , "blood flows from it" .)