Prepare a solution of 5 ml of concentrated sulfuric acid and 100 ml of water. The solution is cooled and add a few crystals of potassium persulfate (sodium). We may not have it, just some other strong oxidizing agent such as potassium permanganate or potassium dichromate (0.5 g per 100 ml). In these cases, however, sometimes takes more than an attempt to put into operation. In this solution we place a drop of mercury and well-refined steel wire (just too thin nail) touching it. Touching must be quite light, preferably a wire then a little delay. First, drop all sorts of turns and moves, with the right touch, however, will quickly shrink and stretch the regular fast movement, reminiscent of the throbbing heart. Fasten the wire at this position pulsate "heart" longer. Unless the movement is now, adding to the solution a few crystals peroxidisíranu.