The most common and most likely answer to this crossword clue is the 6 letter word ANGINA
I've seen this crossword clue in The Guardian
A
N
G
I
N
A
More clues leading to the result ANGINA
- Hearty complaint from gang in Arbroath
- An alcoholic drink goes with a medical condition
- Girl defending Joe's heartfelt complaint?
- Being suspended, first and last just so, a stabbing pain
- New trap given room by motorists – it’s a dreadful pain
- Once clothing removed, managing to treat disorder
- After a liaison’s end, woman’s heartache
- Alcoholics Anonymous name spirit involved in heart disease
- Chest complaint treated again with nitrates, primarily
- An alcoholic drink leads to a complaint
Buddy explains!

The straight part
We know that "heartache" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heartache = angina.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ANGINA mean?
ANGINA noun- An inflammatory infection of the throat, particularly quinsy.
- Short for angina pectoris.
- A chest pain or shortness of breath occurring with lesser degrees of arterial blockage.