The 2S31 Vena is the first self-propelled gun-mortar designed by Russia after the end of the Cold War, and is essentially a larger version of the 2S9 airborne vehicle. The 2S31 is based on the chassis of the BMP-3 IFV with some modifications, mainly the removal of crew positions next to the driver (who sits at the front) as well as the rear troop compartment, and the inclusion of a much larger three-man turret. This is equipped with a 120-mm 2A80 gun-mortar, which has a longer barrel than that of the 2S9 but carries the same family of ammunition. For indirect fire, this includes high-explosive munitions with a range of between 2-18 km, as well as a cargo round which carries HE/fragmentation submunitions and a laser-guided projectile with a range of 13-14 km. Direct fire includes the same HEAT rounds that are used by the 2S9 and which have a maximum penetration of 650 mm of steel armor. As with the BMP-3 that it is based on, the 2S31 is fully amphibious thanks to two water jets mounted on the rear hull, and there is also NBC protection. A turret-mounted 7.62 PKT machine gun is provided as defensive armament. The 2S31 entered Russian service in the late 1990s although it is unclear whether it has seen combat: there is no documented use of it in Ukraine thus far. Only two countries, Azerbaijan and Venezuela are known to also operate it.

Developement began using the Obyekt 934 light tank chassis although the eventually it was decided to use that of the BMP-3 instead. It entered service as the 2S31 Vena. No major variants are known to exist.