The invention relates to an inner heat exchanger for high-pressure refrigerants which is also used as an accumulator or refrigerant collector in air conditioning circuits. The inner heat exchanger includes an outer cylinder arranged and an inner cylinder arranged therein. The inner cylinder is designed as a bent flat sheet or tube with microchannels for refrigerant under high pressure. The liquid refrigerant under low pressure is collectable within the inner cylinder. Between inner cylinder and outer cylinder are formed channels in which the vaporous refrigerant under low pressure flows from a low-pressure inlet to a low-pressure outlet.