 Heart failure is an abnormality of cardiac structure or function leading to failure of the heart to deliver oxygen at a rate commensurate with the requirements of the metabolizing tissues, despite normal filling pressures or only at the expense of increased filling pressures. The commonest causes are hypertension or ischemic heart disease. If this definition holds, then heart failure should be associated with some measure of reduction in inotropy or oxygen delivery. Until recently there was no simple non-invasive, bedside test that could aid the assessment of patients with heart failure. Whilst inotropy or myocardial contractility as a concept is well known to all clinicians, it is seldom thought of as a measurable quantity. 