I am going to publish a series of posts about issential heart sound and murmurs. I will try to be explicit and breaf. And I will try to give information relevant to clinical use.
The first heart sound will be the first. This is natural, isn't it?

Listen to this audio:

This is a first heart sound (S1) only.  Read further, and you will understand everything about it.  Some minutes later.   

The first heart sound marks the moment when diastole ends and systole begins; the moment when mitral and tricuspid valves close.  

The beginning of systole is a great event in the frame of the cardiac cycle: the powerful ventricles' myocardium begin to contract, a big mass of the blood begins to move.  It can not be a silent event!  But so tiny structures as mitral and tricuspid valves create the major part of loudness of S1 while closing.  The pillow can be a big stuff, but we are not able to make a loud bright sound with it.  But with a tiny string we can.          

The closing of mitral and tricuspid valves is not simultaneous.  Normally mitral valve closes first.  The tricuspid valve closes slightly later.  That is why S1 is not a single sound.  Actually, S1 consists of two sounds which are called mitral component (M1) and tricuspid component (T1).  Look:

This is a recording of normal S1 you have just heard.  Every another sound was removed.  You can clearly see two components of S1.

Below there is the corresponding audio with S1 only.  Listen to it again and note two components of S1:

Every time while listening every patient we must pay careful attention to two components of S1.  It matters.  Now listen to the original recording of this patient.  Try to find S1 and his components.  Use headphones.  If you can not take this recording in, read this post.  You will find there vital, but fortunately simple rules, without which cardiac auscultation becomes impossible.      

In the next posts, I will explain how to analyse S1.