: lacking courage : fainthearted.

How do you describe a weak heart?

without courage or fortitude; fainthearted.

Is not for the weak hearted?

The definition of not for the faint-hearted in the dictionary is If you say that something is not for the faint-hearted, you mean that it is an extreme or very unusual example of its kind, and is not suitable for people who like only safe and familiar things.