1.01. S1, S2, and the Cardiac Cycle.

Cardiovascular system reveiew for the USMLE Step 1 exam.

• Two main heart sounds are s1 and s2, also known as "lub" and "dub"
• S1 corresponds to closure of the mitral and tricuspid valves
• S2 corresponds to closure of the aortic and pulmonic valves
• The pause between s2 and s1 is longer than the pause between s1 and s2 in a normal cardiac cycle
• Elevated heart rate can make it harder to distinguish the two sounds
• The noise produced by the valves slamming shut, like a door being slammed shut
• The Atria contracts before the ventricles, and the mitral and tricuspid valves separate the atria from the ventricles, so they shut first which produces S1
• The ventricles contract and push blood through the aortic and pulmonic valves, and These shut after this event producing S2.