A 40 year old male was brought to the hospital with acute pain in the upper abdomen. Pateint was in shock with feeble pulse and tachycardia. There was tenderness present in the epigastrium. There is no blood in the gastric aspirate and thepatient felt better after aspiration. X-ray abdomen showed no free gas under the diaphragm. Investigations revealed TLC 13500 serum bilirubin 2.0 mg and serum amylase 800 I.U. The most likely diagnosis is -