Impulse of heartbeat originates from:
1. S.A. Node
2. A. V. Node
3. Vagus Nerve
4. Cardiac Nerve

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

1. Purkinje system

2. Sinoatrial node

3. Atrioventricular node

4. Atrioventricular bundle