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

Explanation

## 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.