How do I enable the Health/Hearts Shield?

As a Duolingo Plus subscriber, you have the option of enabling the Health shield. This way, you won't lose Health bars for an incorrect answer while in a lesson. To turn on the shield, follow these easy steps: 

1. Make sure you have the latest Duolingo app version.
2. Open your Duolingo app and tap on the "Health" tab (it will have a large heart icon).
3. Tap the Unlimited Plus.
4. Now you should be able to make mistakes without losing any health.