2 questions....
 

My first question is how does one get their heart rate up if they are on medication to prevent your heart rate from rising? Second question is if you had 15 minutes to exercise what would you be doing? I know the typical squats, lunges and crunches but any others?

Don't know about the first question, but if I had only 15 minutes to exercise I alternate between flipping a tractor tire across a parking lot and beating said tire with a sledgehammer or weighted club.