The cardiac pacemaker in a patient fails to function normally. The doctors find that an artificial pacemaker is to be grafted in him. It is likely that it will be grafted at the site of -

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.