In this study, patients presenting within the first 48 hours of an acute ischemic stroke (i.e., a blockage of one of the arteries supplying a part of the brain) will be randomly assigned to either of (1) a 1-hour treatment of external counterpulsation (ECP) applied at a pressure that is typically therapeutic, or (2) a 1-hour treatment of ECP at a minimal pressure in a control group. ECP-induced changes in brain artery flow velocity will be assessed with an ultrasound prior to and then during ECP in each group, and an optimal pressure that results in an augmentation of flow velocity will be determined. A neurological exam will be performed prior to, during, and after ECP in each group, in order to assess any changes in stroke symptoms related to ECP. Patients will be followed to 30 days. The main goal of this trial is to evaluate if ECP is safe and feasible to use as a treatment for stroke. In addition, the trial will enable an assessment of whether or not ECP increases blood flow to the brain or affects the neurological symptoms of a patient with a stroke.