Almost 50 years ago,we published detailed hemodynamic findings in a patient with heart failure and intermittent left bundle branch block.Delayed intraventricular conduction was consistently accompanied by an increased duration of left ventricular(LV)isometric contraction,a drop in systolic blood pressure,a rise in heart rate,and a drop in cardiac output.To our knowledge,this observation provided the first ever evidence that delayed mechanical LV contraction was associated with deterioration,and return to a normal pre-ejection phase with improvement in LV function. Almost 50 years ago, we published detailed hemodynamic findings in a patient with heart failure and intermittent left bundle branch block. Delayed intraventricular conduction was consistently accompanied by increased duration of left ventricular (LV) isometric contraction, a drop in systolic blood pressure, a rise in heart rate, and a drop in cardiac output. To our knowledge, this observation provided the first ever evidence that delayed mechanical LV contraction was associated with deterioration, and return to a normal pre-ejection phase with improvement in LV function.