Could this also mean: "The two men are in (cardiac) arrest." ?
Yes but in this case, you must write complete "I due uomini sono in arresto cardiaco." "The two men are in cardiac arrest."
Both of them? Together? What can they have been doing?
non capisco perché si dice "I due uomini" invece di "gli due uomini" considerando che sarebbe gli uomini e non "i uomini" perché la parola uomini comincia con una vocale. Cosa sta succendo in questo caso?
As you said, we say 'gli uomini' because it starts with a vowel, but here you have the word due, and that starts with a consonant :)
what's wrong with 'in detention' rather than 'under arrest'??
Is the 'under' implied?
That's just how we say it in English - you can be 'arrested', and you can be 'under arrest' (but you can't be 'in arrest' or any other alternatives, in this context).
I put 'two men' instead of 'The two men' and it was marked wrong. Am I wrong?