Well after reading the Paleo solution i have a question about cardio. I somehow got the
idea that it's not healthy to do cardio, in the 40-50 percent range. But when i go to work
on my motor bike or when i have long walks, with my wife my heart rate will definitely
elevate to 40-50 percent i have tested with a heart monitor.What do you think?

What exactly did you read in the Paleo Solution? I've read a bunch of Mark Sisson's works, but not the book in its entirety.

I suspect you're alluding the the alleged "Fat Burning Zone" that's on all cardio machines since 1930 or so. That is, when you're working in the 65-ish percent of your VO2 Max, you're supposedly burning the most amount of fat per the least amount of muscle. However, this has long been debunked for the general public as being the go-to solution for optimal fat loss. Why? Because it's so damn slow and ineffective.

However, just because it's sub-optimal doesn't mean it's unhealthy. Cardio is good for you. Any type of exercise is good for you.

If you are having heart problems, you might want to stop force feeding yourself candied quail eggs with a toilet plunger.