Muscle Strain or Overuse: This is the most likely diagnosis given the history of heavy lifting for a couple of hours before the onset of pain. The pain is likely due to muscle fatigue or strain, which can cause radiating pain or a sensation similar to electric shock.

Neuralgia or Nerve Irritation: Heavy lifting can irritate nerves in the arm, leading to pain that feels like electric shocks. This could involve the radial or median nerves, which run through the areas mentioned.
Tendinitis: Inflammation of the tendons around the elbow or forearm, which could be exacerbated by heavy lifting, might cause pain that radiates down the arm.
Cervical Radiculopathy: Although less likely given the specific location of pain, cervical radiculopathy (nerve root irritation in the neck) can cause pain and sensations down the arm, including the area from the bicep to the mid forearm.

Acute Compartment Syndrome: Although rare, this is a medical emergency that requires immediate attention. It involves increased pressure within a muscle compartment, which can lead to nerve and muscle damage. Pain out of proportion to what is expected and pain on passive stretching are red flags.
Vascular Injury: Injury to the blood vessels from heavy lifting, although unlikely, could lead to ischemia or other vascular complications, presenting with pain.

Peripheral Nerve Entrapment: Conditions like radial or median nerve entrapment could cause symptoms but are less common and usually have additional symptoms like numbness or weakness.
Electrolyte Imbalance: Certain electrolyte imbalances can cause muscle cramps or spasms that might feel like electric shock pains, but this would typically be associated with systemic symptoms or other muscle groups.
Neuropathic Pain Syndromes: Conditions like complex regional pain syndrome (CRPS) are rare and could present with burning or shock-like pains but usually follow a distinct injury and have other characteristic symptoms.