I train - bodybuilding style - 5 times a week and I do cardio for 15 minutes after each workout.
I keep my heart rate between 130 - 140 bpm for the entire 15 minute session.
At that level, I can have a conversation with the person next to me without huffing or puffing.
Most of the time, I see would-be body builders in the gym doing what they call "cardio" way way to intensely.
There is no need for your heart rate to be above 150 bpm if you are doing your cardio.
For that matter, unless you are dieting for a show and cutting, no more than 20 minutes per session is all most folks would need to keep their ticker in a nice aerobic range.
Intense cardio and long sessions increase cortisol in the blood. That has been proven over and over in published medical research. Cortisol has a negative impact on protein synthesis and will curtail muscle hypertrophy.
Regards.
.