- The sinoatrial node, or SA node, located in the right atrium near the entrance of the

- 竇房結或SA結點，位於右心房

superior vena cava.

接近上腔靜脈的入口。這是自然天生的心臟激搏器。它促發心跳

This is the natural pacemaker of the heart.

並決定心臟率。從竇房結釋放的電脈衝 傳遍兩個心房，

It initiates all heartbeat and determines heart rate.

並刺激它們收縮。 - 房室結或AV結點，位於

Electrical impulses from the SA node spread throughout both atria and stimulate them to

在右心房的另一邊，靠近 在AV瓣膜。 AV結點作為

contract.

一個電通道通往心室。它延遲電脈衝到心室的傳輸。

- The atrioventricular node, or AV node, located on the other side of the right atrium, near

這種延遲是為了確保在心室收縮前，

the AV valve.

心房已將所有的血液擠入心室。 - AV結點接收了SA結點的訊號，

The AV node serves as electrical gateway to the ventricles.

並將它們傳遞到房室束（atrioventricular bundle） - AV束（AV bundle）或希氏束（bundle of His）。

It delays the passage of electrical impulses to the ventricles.

- 這個房室束接著分為左右 束網，將電脈衝

This delay is to ensure that the atria have ejected all the blood into the ventricles

傳向心臟的頂部。此訊號接著又被 傳遞到浦金氏纖維（Purkinje fibers），

before the ventricles contract.

並方向改由下往上，擴散到整個心室的 心肌。

- The AV node receives signals from the SA node and passes them onto the atrioventricular

心臟的電活動可以心電圖的形式紀錄，

bundle - AV bundle or bundle of His.

ECG或稱EKG。心電圖複合式記錄 由結點和心肌細胞產生的

- This bundle is then divided into right and left bundle branches which conduct the impulses

所有動作電位。心電圖的每個波 或波段對應於

toward the apex of the heart.

心電的某個事件週期。

The signals are then passed onto Purkinje fibers, turning upward and spreading throughout

當心房充滿血液，竇房結啟動，電訊號傳遍

the ventricular myocardium.

心房並促使它們去極化。這個 階段由心電圖的 P波呈現。

Electrical activities of the heart can be recorded in the form of electrocardiogram,

心房收縮始於P波開始的100毫秒的之後。

ECG or EKG.

PQ段表示訊號從SA結點傳到AV結點的時間。

An ECG is a composite recording of all the action potentials produced by the nodes and

QRS波群表示AV結點的啟動 和心室的去極化：

the cells of the myocardium.

- Q波對應室間隔（interventricular septum）的去極化。

Each wave or segment of the ECG corresponds to a certain event of the cardiac electrical

- R波是由心室大部份心肌的去極化所形成。

cycle.

- S波代表心室去極化的最後階段。

When the atria are full of blood, the SA node fires, electrical signals spread throughout

心房的再極化在同時間發生，但它的訊號被

the atria and cause them to depolarize.

更強大QRS波群蓋過。 ST段反映了心肌動作電位

This is represented by the P wave on the ECG.

的穩定階段。這時心室收縮並打出血液。

Atrial contraction , or atrial systole starts about 100 ms after the P wave begins.

T波表示心室心肌放鬆或稱心室舒張前

The P-Q segment represents the time the signals travel from the SA node to the AV node.

的在極化。這樣的週期在每次的心跳循環重演。

The QRS complex marks the firing of the AV node and represents ventricular depolarization:

- Q wave corresponds to depolarization of the interventricular septum.

- R wave is produced by depolarization of the main mass of the ventricles.

- S wave represents the last phase of ventricular depolarization at the base of the heart.

- Atrial repolarization also occurs during this time but the signal is obscured by the

large QRS complex.

The S-T segment reflects the plateau in the myocardial action potential.

This is when the ventricles contract and pump blood.

The T wave represents ventricular repolarization immediately before ventricular relaxation,

or ventricular diastole.

The cycle repeats itself with every heartbeat.