Shiva is often depicted with an “hourglass drum” or Damaru. The Damaru symbolises the sound of creation, the mystic ॐ, or Aum.
In the Nataraja Shiva holds a damaru in one hand to represent creation and fire in another to represent destruction. The drum beats out both the heartbeat of the smallest animal and of the aeons long cycle of the creation and destruction of the universe.
The drum, when viewed from the side has the appearance of two overlapping triangles, which like the shatkona represents the masculine and feminine aspects of God, the Shiva-Shakti.