External counterpulsation is a noninvasive method of applying external pressures to vascular beds of the lower extremities synchronous with the cardiac cycle. Numerous animal experiments and a number of clinical trials have been conducted over the years in patients with various forms of cardiac disease to evaluate the effectiveness of external counterpulsation. The external counterpulsation machines (known as ECP and EECP machines) are currently widely available for use in the treatment of angina by applying positive pressure to the lower extremities during cardiac diastole to increase coronary flow. External counterpulsation has also been shown to be capable of perfusing the ischemic myocardium following an AMI and of assisting the failing left ventricle in patients with CHF. In these applications, positive pressure is applied externally to the lower extremities during cardiac diastole and negative pressure during cardiac systole so as to increase coronary flow and reduce the work of the heart. This paper provides a review of the developments in the area of external counterpulsation and the related devices. The paper also reviews the experimental evidence that provides the scientific basis for the design of a device now under development and called external left ventricular assist device (XLVAD) that should provide effective support of the left ventricle of a patient in congestive heart failure or following an AMI. The evolutionary development of the external counterpulsation devices into the XLVAD is presented in detail. The clinical and mechanical advantages as well as the shortcomings of each device are described.