S1 consists of the simultaneous closure of Mitral and Tricuspid valve.

It is a low frequency sound, occurring at the beginning of systole. 

Its best heard over the apex

The S1 can have many variations which could hint to the diagnosis.

Types of S1

1. Loud S1
   1. Mitral stenosis
   2. Sinus tachycardia
   3. Hyperkinetic circulation due to fever, anaemia, exercise
   4. Short PR interval- tachycardia, nodal rhythm
2. Soft or muffled S1
   1. Mitral incompetence
   2. Prolonged PR interval (heart block)
   3. Calcified mitral or tricuspid valve
   4. Obesity
   5. Emphysema
   6. Pericardial effusion

Splitting of S1

• Wide splitting in
• Complete Right Bundle Branch Block
• Left ventricular pacing
• Ebstein anomaly

Reversed splitting of S1

• Generally seen in
• Left Bundle Branch Block
• Severe Mitral stenosis
• Left atrial myxoma