These two layers are separated by a thick film of fluid that acts like a natural lubricant, providing a slippery environment for the heart to move around in so it doesn't create friction as it beats.

这两层被一层厚厚的液体膜隔开，液体膜就像天然润滑剂，为心脏的运动提供了一个光滑的环境，这样它就不会在跳动时产生摩擦。