A 40year old male was bought to the hospital with acute pain in the upper abdomen. Patient was in shock with feeble pulse and tachycardia. There was tenderness present in the epigastrium. There is no blood in the gastric aspirate and the patieny felt better after aspiration. XRay abdomen showed ni free gas under the diaphragm. Investigation revealed TLC 13500 serum bilirubin 2.0 mg and serum amylase 800IU.The most likely diagnosis is