A study of patients with and without acute coronary syndrome (ACS), a group of symptoms caused by occluded coronary arteries, showed significant differences in blood viscosity between the two groups. Those with ACS, defined by unstable angina or myocardial infarction, had 29.2% (p = 0.016) higher low-shear blood viscosity and 15.6% (p = 0.036) higher high-shear viscosity than those without ACS. Because most whole blood viscosity samples used in clinical studies are drawn from peripheral vessels, the researchers compared coronary artery samples to peripheral samples. This helped identify the applicability of these viscosity findings within arteries clinically relevant to ACS, the coronary arteries. Whole blood viscosity was not different between coronary artery samples and peripheral samples.