Purkinje fibres, AV bundle, AV valve, SA node.

Explanation

To determine the correct order of electrical impulse generation and conduction in the heart, we need to understand the role of each component mentioned in the question: SA node, AV bundle, AV valve, and Purkinje fibers.

### Step-by-Step Solution:

1. **SA Node (Sinoatrial Node)**: The process begins at the SA node, which is located in the right atrium. The SA node is known as the natural pacemaker of the heart, as it generates electrical impulses that initiate each heartbeat. This is the first step in the conduction pathway.

2. **AV Node (Atrioventricular Node)**: After the SA node generates an impulse, the electrical signal spreads through the atria, causing them to contract and push blood into the ventricles. The impulse then reaches the AV node, which is located between the atria and ventricles. Here, the signal is delayed to allow the ventricles to fill with blood before they contract.

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