Ultrasound (US) with a frequency above 20 kHz is an important tool for medical diagnostics and therapy, especially in the study and treatment of diseases of the circulatory system. Based on an analysis of modern research, this article summarizes the biological effects of ultrasound on blood vessels, blood cells, and blood flow. The main mechanisms of action are considered, including thermal effects, cavitation, and mechanical influences, as well as their consequences for the vascular endothelium, erythrocytes, platelets, and leukocytes.