[Serie: All About Japanese Particles]
*1. Usually used at the end of a sentence, indicating resentment or complaint.
お知らせ下されば、病院へお見舞いに参りましたものを。。。
Oshirase kudasareba, byōin e omimai ni mairimashita mono o.
If only you had told me, I would have come to see you at the hospital.
私にできることでしたら、お手伝いしましたものを。。。
Watashi ni dekiru koto deshitara, otetsudai shimashita mono o …
If there had been something I could have done, I would have helped out.
– Source: All about particles – A handbook of Japanese function words –