in the heat of the moment—at the moment of the greatest emotional excitement:
- Small as she was, she looked as though in the heat of the moment she might hit him.
on the spur of the moment—acting on a sudden impulse; without deliberation:
- The crime of jealousy committed on the spur of the moment, makes poor material.
Note: The expression does not correlate in meaning with the phrase on the spur—(UK dated) at full speed; with the utmost haste:
- The servant rode away on the spur, to alarm the family at the mansion-house.