Emotions of fear, tension or happiness can be quantitatively measurable using a method that calculates a measure called scaling exponent (SI). The measure SI is computed from consecutive pulse data approximately 2000. The methodology is heartbeat interval timeseries analysis. The name is the modified detrended fluctuation analysis (mDFA). This book introduces how the methodology works. Experimental evidences shown are obtained from neurobiological, mainly electrophysiological investigations on invertebrate animals and humans. The heartbeat carries something that cannot be seen from outside. mDFA reveals it. Knowing what's happening behind the heartbeat is reading internal world of us. Checking the heart may be possible to prevent disaster before crisis. The quantifying method will reinforce safety and security applications if it will be incorporated into a gadget although an accurate 2000-beat data-logger has not yet been develop.