Conducting System of Heart

The human heart is myogenic: the heart beat starts in the heart muscle itself.
The sinoatrial (SA) node, a patch of nodal tissue in the right upper corner of the right atrium, generates the maximum number of action potentials (70–75 per minute). It initiates and maintains the rhythm of the heart, so it is called the pacemaker.
From the SA node the impulse spreads through the atria to the AV node, then along the bundle of His (AV bundle) and the Purkinje fibres to the ventricles. These parts conduct the impulse but do not normally set the rhythm.
When the natural pacemaker fails, the artificial pacemaker takes over its function. So it is placed to act at the site of the sinoatrial node.
So it will be grafted at the site of the sinuatrial node.

The conducting system of the heart (SA node, AV node, bundle of His and Purkinje fibres) is made of specialised (modified) cardiac muscle fibres, not nerve fibres. The heart is myogenic.
The bundle of His (AV bundle) starts from the AV node, passes through the interventricular septum, and divides into right and left bundle branches, which give rise to the Purkinje fibres spreading throughout the ventricular walls.
So it carries the impulse only to the ventricles; the atria receive the impulse directly from the SA node through the atrial muscle.
So the bundle of His is a network of muscle fibres found only in the ventricle wall.