Two questions.

1. If you have a low % body fat, will your body go into survival mode and slow down your metabolism? So even if you're packed with muscle would it then be extremely easy for the body to pack on more weight and thus fat?

and

2. Is it possible to have a low resting heart rate (say 40bpm) and have a weak heart? Someone told me ou can get a low RHR with hours of low intensity cardio, but still have an unhealthy heart compared with if you'd done high intensity cardio. That seems complete bs to me but just wanted to make sure.
To me, a heart has a low RHR when it's strong and can therefore pump more blood in one beat. Was the guy who told me that you could still have a weak heart doing low intensity cardio full of crap, or was he just implying that it's impossible to get a low RHR with low intensity cardio.

My reply to #1: what?

My reply to #2: what is a weak heart?
the lower your resting heartrate is, that better.
although, if your resting hr is lower than lance armstrong's, that's cause for concern. his is low 30s.
HIIT will lower your resting HR faster over time than LISS will.