I don't think it has anything to do with RBB or LBB, this is just structures (pathways) in your heart I think :)
The down "tip" of
your heart (I think it's named Apex) tends to push against your chest
wall when laying on the left side
. The heart looks a bit like a giant strawberry.
In addition, some arteries are closer to your skin on left side
, making pulsations much more noticeable when your body weight push against them.