Heart failure affects more than 6 million people in the United States, and the number increases by more than 0.5 million every year. Acute decompensated heart failure accounts for over one million hospital admissions per year, and the estimated direct and indirect cost for heart failure in 2008 is more than $30 billion. Cardiac resynchronization therapy (CRT) has been approved by FDA as a treatment of heart failure patients refractory to conventional therapy. However, 20-40% of the patients who selected for CRT based on the conventional criteria do not respond to CRT. We developed a quantitative technique, phase analysis, which automatically measure left ventricular dyssynchrony from gated myocardial perfusion SPECT studies. We have validated this technique and shown that it can reproducibly predict the response to CRT in patients with heart failure induced conduction disturbances and ventricular dyssynchrony. This technique has been introduced on the First Taiwan Nuclear Cardiology Symposium. This special review is a follow up of the lecture.