In response to your questions,
1. when you increase your heart rate during a workout--that's typically the goal in cardio--you burn more calories. 6 beats above your target is not that drastic--imo. It would equate to you getting a more intense cardiac workout and thereby burn more calories.
2. Were you experiencing indigestion? This happens to me often when I do cardio, which is why I began to take an over the counter Zantac and a couple of Tums chewables everyday. Depending on what I have eaten, it makes or breaks my cardiac workout. I can't stand that feeling, and I drink plenty of water before, during, and after cardio.
Hope this helps