The cardiovascular system is more than a biological pump and a system of pipes. Unlike a typical plumbing system, the human body actively changes the size of its pump and pipes through a process of mechanotransduction. Understanding this process at a cellular level enables a greater understanding of the entire system at a fundamental level. This chapter focuses on studies using flexible polymer microposts, which can measure the contractile forces of cardiovascular cells with nanoscale precision. Specifically, microposts have been used to understand how cardiomyocytes, endothelial cells, and platelets change their function in response to react to changes in their microenvironment and how these changes relate to diseases and disorders of the cardiac, vascular, and coagulation systems.