Assessment of left ventricular (LV) systolic function is the most common indication for performing an echocardiogram and, correspondingly, the detection and quantification of systolic dysfunction hold major implications for patient diagnosis and management. However, no perfect measure of ‘systolic function’ exists and there are fundamental limitations inherent to all currently available surrogates. In this clinically focussed editorial, we examine what can actually be measured by echocardiography, identify the techniques with established practical utility and consider their current and potential roles in guiding clinical practice. What can be measured by echocardiography? The physiological parameter that most accurately represents systolic function is contractility - the ability of myocardium to contract against a specific load for any given preload. Assessment of contractility requires simultaneous and continuous measurement of LV pressure and volume over multiple cardiac cycles with manipulation of preload to generate pressure-volume loops across a range of loading conditions. At present, this can only be achieved accurately by invasive methods using conductance catheters. In contrast, all of the commonly utilised echocardiographic (and other non-invasive imaging) techniques for assessing systolic function measure contraction ‐ essentially the degree of myocardial fibre shortening that occurs during systole. This is dictated by the degree of preceding myocardial stretch (preload) and the pressure against which it contracts (afterload) as well as intrinsic contractile function. Consequently, all techniques based on assessment of contraction provide ‘load-dependent’ measurements of systolic function. Nonetheless, a comprehensive echo study provides important insight into the prevailing loading conditions and integration of this information with the indices of LV contraction informs the overall evaluation of systolic function. It should also be borne in mind that our aim, ultimately, is not to quantify systolic function as a physiological parameter but to detect and grade clinically meaningful systolic dysfunction. It is therefore preferable to evaluate echo-based indices of systolic function against a clinical standard rather than a pure physiological one. Clinically useful measures should ideally correlate with symptoms of heart failure, predict the subsequent development of adverse events and, most importantly, provide a proven basis for therapeutic decision making.