Heart Sounds Heart Sounds| Heart Sounds | Mechanism | Clinical Features |
| Hear a Normal Sound | ||
| First (S1) | M-T valve closure* | Single |
| Second (S2) | A2-P2 valve closure** | Split*** |
| Third (S3) | Early diastole | May be normal |
| Fourth (S4) | Late diastole | Pathologic |
| *Mitral and tricuspid **Aortic and pulmonic ***A2-P2 interval widens with inspiration. |
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