1.2.Cardiac dysynchrony In cardiology, dyssynchrony is the phenomenon in which the different parts of the heart contract in a non-rhythmic physiological sequence, leading to a decrease in ejection efficiency. Left ventricular mechanical dyssynchrony is the differences in the timing of contraction or relaxation between different myocardial segments or the contraction of the heart muscle areas that are delayed in the systole. Mechanical dyssynchronyusually appears in the late stages of some heart conditions, associated with hypertrophy and left ventricular dysfunction.