This is a diagram I made showing Tummo's affects on the chakras. Tummo is Vajrayana inner heat yoga, and I've been practising it for a couple of weeks now with quick results. The smaller, bottom circle is the navel or sacral chakra. When it opens wide, full of light and fire, the energy connects with the heart chakra - the second of the smaller circles - bypassing the solar plexus which acts as a kind of pivot or press on the sacral but doesn't seem to contain a bliss essence drop like the sacral and heart chakras, so remains closed or not part of the Vajrayana system. When both the sacral and heart chakras are wide and full of heat, another circle or centre is formed embracing the two chakras, blending them as one ball of energy. The same happens when the energy connects to the throat, which also has a bliss drop, via the central channel, and a larger ball of energy is created blending the three chakras. It eventually advances to the crown where I imagine the whole body becomes full of light, but I haven't reached there yet. Use a little caution if Tummo appeals to you. Traditionally it should be practiced with a qualified teacher. I'm being guided by Guru Rinpoche and Tara and am extremely grateful, dedicating the practise to the liberation and happiness of all sentient beings. I think it's a beautiful diagram.