Now and again, favourite American shows something from the heart? (5)
I believe the answer is:
aorta
'something from the heart?' is the definition.
I can't judge whether this definition defines the answer.
'now and again favourite american' is the wordplay.
'now and again' means one should take alternating letters (letters taken on a regular basis).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
The alternate letters of 'favourite' are 'aort'.
'aort'+'a'='AORTA'
'shows' acts as a link.
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "sort of vessel" , "Body's main artery" , "Major artery at left of heart" , "Large trunk artery" , "vital transporter" .)