CD34 and ischemia: Repetitive episodes of transient myocardial ischemia are associated with adaptive processes leading to neovascularization.42 Recently, Hammadah et al have shown that patients without ischemia had a 15% increase in CD34+ cells counts after exercise, whereas patients with myocardial ischemia had an 18% postexercise reduction.43 Interestingly, this latter EPC decrease was proportional to the magnitude of ischemia and to the change in circulating levels of a stromal-derived factor (SDF)-1α, a cytokine that stimulates homing of EPCs to the ischemic myocardium.