Which of the following events occurs during the isovolumetric contraction phase of the left ventricle?

Question

Accepted Answer

A. Both aortic and mitral valves are closed; ventricular volume remains constant while pressure increases. ## Isovolumetric Contraction Phase

**Key Point:** During isovolumetric contraction, both the aortic and mitral valves are closed, the ventricle contracts without changing volume, and pressure rises sharply.

### Definition and Characteristics

Isovolumetric contraction is the brief period (approximately 0.05 seconds) between the closure of the mitral valve and the opening of the aortic valve. During this phase:

1. **Mitral valve closes** — as LV pressure exceeds left atrial (LA) pressure
2. **Aortic valve remains closed** — because LV pressure has not yet exceeded aortic pressure
3. **No blood flows in or out** — both inflow and outflow valves are sealed
4. **Ventricular volume is constant** — hence "isovolumetric"
5. **LV pressure rises sharply** — due to myocardial contraction against a fixed volume

### Pressure Dynamics During Isovolumetric Contraction

```mermaid
flowchart TD
  A[Mitral valve closes]:::action --> B[LV pressure > LA pressure]:::outcome
  B --> C[Aortic valve still closed]:::action
  C --> D[LV pressure < Aortic pressure]:::outcome
  D --> E[Isovolumetric contraction begins]:::action
  E --> F[LV pressure rises sharply]:::outcome
  F --> G{LV pressure > Aortic pressure?}:::decision
  G -->|Yes| H[Aortic valve opens]:::action
  G -->|No| I[Isovolumetric contraction continues]:::action
```

**High-Yield:** The pressure rise during isovolumetric contraction is the steepest in the entire cardiac cycle — this is why it is clinically important for assessing LV contractility.

**Mnemonic: "ISO = Same Volume, Both Valves Closed"**
- **ISO** = same/constant
- **Volumetric** = volume
- Both mitral and aortic valves are **closed**

**Clinical Pearl:** The rate of LV pressure rise during isovolumetric contraction (dP/dt) is a sensitive indicator of LV contractile function and is often measured during cardiac catheterization.

![Cardiac Cycle diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3190.webp)

Answer

B. The mitral valve opens while the aortic valve remains closed

Answer

C. Both aortic and mitral valves are open, allowing blood to flow into the aorta

Answer

D. Blood is ejected into the aorta at a constant rate

Which of the following events occurs during the isovolumetric contraction phase of the left ventricle?

Explanation

Isovolumetric Contraction Phase

Definition and Characteristics

Pressure Dynamics During Isovolumetric Contraction

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