The LT vz. 34 was assembled from a framework of steel "angle iron" beams, to which armor plates were riveted. A 3 mm (0.12 in) firewall separated the engine compartment from the crew. A door allowed access to the engine from the crew compartment. It also had ventilation openings that could be closed. The driver sat on the right side using a 300 by 75 millimetres (11.8 in × 3.0 in) observation port protected by two flaps. The inner flap had an episcope with a 25° field of view. It was connected to the armored outer flap so that opening one closed the other. The outer flap had a 3 mm (0.12 in) slit. To his right was a vision slit 120 by 3 millimetres (4.72 in × 0.12 in) protected by 50 millimetres (2.0 in) of bulletproof glass. The inner flap was padded so that the driver could rest his head on it when driving. The radio operator sat on the left and had his own 120 by 50 millimetres (4.7 in × 2.0 in) vision port with 50 millimetres (2.0 in) of bulletproof glass and an armored shutter. His radios were mounted on the left wall of the hull. The hull machine gun was between the driver and radio operator in a ball mount with 30° of traverse. It could elevate 25° and depress 10°. Most of the machine gun's barrel protruded from the mount and was protected by an armored trough. The mount had a spotting telescope or open sights could be used if the plug at the top of the ball mount was removed. If necessary the driver could lock the mount into position and fire it himself using a Bowden cable.
The turret ring had a diameter of 1.265 metres (49.8 in). The turret sides were 15 mm (0.59 in) thick and its roof had a thickness of 8 mm (0.31 in). The turret was manually traversed (3° per rotation of the handle), but the gearing could be disengaged to allow the commander to shoulder the turret around as desired. The turret had a flat face in the center of which was mounted the 3.72 cm (1.46 in) main armament. On the right side was another 7.92 mm (0.312 in) machine gun in a ball mount. The commander had four episcopes in his cupola and a monocular mirror, 1.3 x 35° periscope which he could extend once he removed its armored cover in his hatch for vision while "buttoned-up". This meant that the commander was responsible for loading, aiming and firing the main gun and the turret machine gun while simultaneously commanding the tank.
The vertical front and side armor was 15 mm (0.59 in) thick, the slanted plates had a thickness of 12 mm (0.47 in), the engine hatch was 10 mm (0.39 in) thick and the top and bottom plates were 8 mm (0.31 in) in thickness. This was deemed enough to deflect armor-piercing 7.92 mm (0.312 in) bullets fired from distances greater than 75 metres (82 yd).
The 6.08 litres (371 cu in), water-cooled, 62.5 horsepower (46.6 kW), inline 4-cylinder Praga engine used a gasoline-alcohol mix. It had a top speed on the road of 30 kilometres per hour (19 mph) and about 15 kilometres per hour (9.3 mph) cross-country. One 64.5 litres (17.0 US gal) fuel tank was located on each side of the engine. The transmission had four forward gears and one reverse gear to drive the front-mounted drive sprockets.
The suspension was an enlarged and modified version of that used in the Carden-Loyd tankettes. It consisted of two small road wheels fastened together on a frame, two frames paired and sprung by leaf springs that made a wheel carrier, two wheel carriers per side. The track was guided by two return rollers and wooden, metal-lined frames. The rear-mounted idler wheel was used to adjust track tension. It had a ground pressure of only 0.5 kg/cm2. It could cross a ditch 2 metres (6.6 ft) wide, climb an obstacle .8 metres (2.6 ft) high and ford a stream .8 metres (2.6 ft) deep. It could uproot trees .18 metres (7.1 in) thick and breach a wall .5 metres (20 in) thick.
The main armament was a Škoda ÚV vz. 34 (A3) gun with a pepperpot muzzle brake and a prominent armored recoil cylinder above the barrel. It fired a .815 kilograms (1.80 lb) armor-piercing shell at 690 metres per second (2,300 ft/s). It was credited with penetrating a plate inclined at 30° from the vertical 37 millimetres (1.5 in) thick at 100 metres (110 yd), 31 millimetres (1.2 in) thick at 500 metres (550 yd), 26 millimetres (1.0 in) thick at 1,000 metres (1,100 yd), and 22 millimetres (0.87 in) thick at 1,500 metres (1,600 yd). Another source quotes penetration of a vertical plate 45 millimetres (1.8 in) thick at 500 metres (550 yd). The machine gun's ball mount could be coupled to the main gun or used independently. Both weapons could elevate 25° and depress 10°. They both used 1.25x power sights with a 25° field of view. The tank used Zbrojovka Brno ZB vz. 35 heavy machine guns in both ball mounts.