<prompt> 2nd hea sound is due toClosure of AV valvesClosure of aoic valveInthrushing of bloodAtrial contraction  <response>: The second is a shoer, high-pitched dup second sound, caused by vibrations associated with the closure of the aoic and pulmonary valves just after the end of ventricular systole.Ref: Ganong;s Review of medical physiology 25th edition. Page: 542 