Soon after anesthetization a 55-year-old patient reported severe weakness, retrosternal pain that irradiated to his left arm and scapular region, palpitations. Objectively: the patient is conscious, adynamic, pale, the forehead is covered with cold sweat. AP- 90/60 mm Hg, cardiac sounds are muffled, the pulse is thready and arrhythmic. What condition developed in the patient?