Cardio while on Reta

Do as much cardio as your goals require, man.

I do cardio five days a week while cutting and haven't lost any muscle. I'm also not very big, lol.

What does Reta have to do with keeping a healthy cardiovascular system?

Same amount. Reta doesn't really alter your cardio needs — do what your goals and recovery allow.

Reta can raise your resting heart rate and increase your need for electrolytes and fluids. I'd say hydration and monitoring cardio become more important when you're taking Reta.