Heavy submachine gun is a term sometimes used to describe Submachine guns that act as support weapons. Typically, submachine guns that are described as "heavy submachine guns" will be large in size and fitted with a bipod, and may even be chambered in a more powerful pistol round or belt-fed in some instances.
The Austro-Hungarian Standschütze Hellriegel, made in 1915, was a machine gun chambered for 9mm Steyr rounds. It was fed by a drum magazine with a flexible connector and had a water cooling jacket. Although the term "submachine gun" had not yet been coined in 1915, the Standschütze Hellriegel is an example of a "heavy submachine gun".
Also in 1915, the Italian Villar-Perosa twin-barreled submachine gun was developed, although it was deployed as a support weapon with spade grips. It was top-fed through two box magazines. In 1918, the OVP submachine gun was introduced, which was basically a single-barreled Villar-Perosa minus the spade grips, that was more suited as an infantry weapon.
The first prototype of the Thompson submachine gun, the "Persuader", was "tape" belt-fed, but it could never fire more than 6 or 7 shots consecutively without jamming. In 1923, a version of the Thompson was designed that had a heavy barrel and bipod, It fired the more powerful .45 Remington-Thompson cartridge which fired a heavier 250-grain (16.2 gram) bullet at higher muzzle velocities of about 1,450 fps (440 m/s), with greater range than the .45 ACP round. Although it was trialed with several armies, it never saw service. It was intended to be a competitor to the BAR.
In 1943, Aimo Lahti developed the AL-43, a variant of the Suomi SMG but intended as a light machine gun chambered in a more powerful 9x35mm round (later in 7.62x35mm) which made it ballistically comparable to the StG-44. It came with a bipod and was a large heavy weapon for a submachine gun.
The Czech ZK-383 was a submachine gun that was very large and heavy, and required a bipod to fire effectively. It has a slow rate of fire and could be used as a fairly accurate light support weapon. It saw quite widespread military usage, from about 1938 - 1970.