Q.Pacemaker is

The SA node is the heart's natural pacemaker because it generates the highest rate of spontaneous electrical impulses, setting the rhythm for the whole heart.

The mammalian heart possesses a specialised, unique conduction/nodal tissue that can generate action potentials spontaneously without any external (neural) stimulus. This system includes the sino-atrial node (SA node), the atrioventricular node (AV node), the bundle of His, and Purkinje fibres.

• The SA node, located in the right atrial wall, is capable of generating the maximum number of action potentials per minute, i.e. the fastest spontaneous rhythm, and so it sets the pace for the whole heart, hence it is called the pacemaker. …

The pacemaker (SA node), located in the wall of the right atrium, spontaneously generates the electrical impulses that initiate each heartbeat and set the intrinsic rhythm of the heart.

The sino-atrial (SA) node, often called the natural pacemaker of the heart, is a small mass of specialised, autorhythmic cardiac muscle tissue located in the right atrium's wall. It generates electrical impulses spontaneously and rhythmically, without any external nervous stimulus, and this impulse spreads through the atria and then to the atrio-ventricular (AV) nod …

The SA-node is called the pacemaker of the heart because it spontaneously generates the electrical impulses that set the rhythm and rate of the heartbeat.

The sinoatrial (SA) node, a mass of specialised, nodal (autorhythmic) tissue located in the wall of the right atrium, can generate its own action potentials faster than any other part of the cardiac conduction system (which also includes the AV node, bundle of His, and Purkinje fibres). Because it dictates the timing of every normal heartbeat, the SA-node is called the pacemaker of …

The sino-atrial (S.A.) node initiates and sets the rhythm of the heartbeat, so it is called the natural pacemaker of the heart.

The heart's own conduction system consists of specialised, modified cardiac muscle:

• S.A. node — located in the wall of the right atrium near the opening of the superior vena cava. It generates rhythmic electrical impulses on its own (~70–75 beats/min in a resting adult) without needing external nervous stimulation, and this impulse spreads through both atria causing them to contract. Because it sets the pace for the entire heart, it is the pacemaker.
• A.V. node — located at the base of the right atrium; receives the impulse from the S.A. node and, after a brief delay, passes it on. …