The most common and most likely answer to this crossword clue is the 17 letter word ELECTROCARDIOGRAM
I've seen this crossword clue in The Times
E
L
E
C
T
R
O
C
A
R
D
I
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A
M
Buddy explains!

The straight part
We know that "One checks pulse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one checks pulse = electrocardiogram.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 ELECTROCARDIOGRAM mean?
ELECTROCARDIOGRAM noun- The visual output that an electrocardiograph produces.