A patient with ischemic heart disease and exertional angina pectoris complains of a sudden constricting retrosternal pain that lasts for over 30 minutes and irradiates to the left arm. The pain occurred during a physical exertion. The pain attack did not stop after the patient had taken 3 tablets of nitroglycerine. On examination, the skin is pale gray, moist, and cold to touch; the facial features are sharp; acrocyanosis is observed; pulse is 102/min., arrhythmic; blood pressure is 90/40 mm Hg. Make the provisional diagnosis: