Pavel talks about this in his Enter the Kettlebell book. He talks about someone named Dr Sears and is the author of the book “The Doctor’s Heat Cure.” He explains that many people think they need to perform exercise for a long period if time to make their heart stronger. However, he states that the more your fitness level improves, the more you should decrease the duration if your training session, ie. <10 minutes of swings. He explains that the natural state of exercise is to get the heart pumping when called to do so. Start the training session at about a level 5 and end it near a 10. For me, what I do is a short warm up ie, a few halos, a swing, clean, press, squat, snatch, and get down. Both left and right. Then I get right into what I plan to perform. Sometimes I forgo the warm uo entirely and just start swinging light and try to hit the different volume knobs of my power in my swing. I think this best conditions the heart to be prepared to take that sudden spike when it happens. My wife is an ER nurse and has to leap up in a moments notice as do many people for their respective professions.