Software Testing/Design Requirements

I am studying how to:

1. State the practical requirements and architectural considerations for the real-time systems and critical systems.

2. Articulate the design approaches specifically geared towards the real-time systems and critical systems.

With this in mind, In reference to a pace-maker as a real-time system,

Q. What are 5 important requirements for it? Please explain why each of these requirements is important.

Thank you!