I don't go by HR to judge cardio intensity. I go strictly by how I feel. I want my cardio to feel like I am pushing it the whole time, but can maintain it. I can speak in short, quick burst, but not entire sentences. I cannot tell an entire story in one breath, lol. I key into how my body feels the entire time - if I feel I can do more, I up the intensity and if I feel TOO tired, I lower it slightly. This is how I weight train too. Some days I can push it more, others I can't.
For HIIT (High Intensity Interval Training) the 'work' interval should be only maintainable for NO MORE than 1 min. The 'recovery' interval should be easy.