@RolloTreadway relevant context depending on where you're located: in the US, the Good Samaritan laws protect you partly, but you can still be sued if the person you try to save is a particularly huge asshole and sufficiently wealthy, and you fuck up somehow.

In most of the rest of the world there is no such risk, and many places (I know this is true for Germany), you can be liable if you don't intervene to save someone's life when you could have. You are not liable for anything if you try to save their life and fail. Don't claim any medical training you don't have, and you're safe. You're still qualified to use an AED.