I guess there is something to be learned about English in this mistake. In English when we say "last night" we all know what that means but it doesn't really make any sense. It couldn't have been the last night if we're having another one today. We more or less use last when describing the finality of something, not that it was previous. We're not even very consistent in English with describing time. "Yesterday" instead of last day. We don't say yesternight or "previous night". But I think прошлои probably means more like "previous" and is more consistent. So by assuming that it means last and can be applied the same way seems wrong.
I do not know. Did you by any chance put the hearts there by yourself (like, videogame "hearts"). Or maybe you were pissed your last life is out...
(the Russian phrase actually means past, as in "previous" life — the life before the one you have now; last as in "the one after which there is none / most recent of all" is последний)