+2 on cutting calories as well as exercising. I had the same problem about a year ago. I had been biking about 1000 miles per year to keep the weight off, but as I got older, the weight came back slowly. I finally started watching what I ate and have lost 30 lbs over the last year. Unfortunately, exercise just isn’t enough.
As far as your heart rate goes, when I am doing 45 second intervals, my heart rate goes to about 175ish (34 years old) and recovers to about 125 in about 20-30 seconds. But I am reasonably fit now. It used to take much longer.