A fastener driving apparatus includes a power source, a control circuit, a motor, a first hollow guide member having a first volumetric capacity, a first piston, a linear motion converter, a second hollow guide member having a second volumetric capacity, a second piston, an anvil, a valve arrangement and at least one sensor. The guide members may have an elliptical or oval cross-section. During a compression stroke, the first piston compresses gas in the first hollow guide member. The valve arrangement opens and communicates the compressed gas to the second hollow guide member, causing the second piston to move the anvil to drive a fastener. During a return stroke of the first piston, the valve arrangement opens, communicating a vacuum created in the first hollow guide member to the second hollow guide member, thereby causing the second piston and the anvil to retract to their initial positions.