Apparatuses and methods for delivering a fluid, including a viscous fluid. These apparatuses may include a fluid reservoir, two or more piston chambers, a manifold, a delivery port, and a drive assembly and may be configured to inject either a predetermined amount of fluid or a continuous stream of fluid. These apparatuses may also be configured to switch between filling, injection and aspiration modes. These apparatuses may generally be hand-held and lightweight and may provide a significant mechanical advantage to the user.