A two-stroke engine for a portable two-stroke engine in a portable handheld work apparatus includes a combustion chamber (3) formed in a cylinder (2). The combustion chamber (3) is delimited by the piston (5) which drives the crankshaft (7) via a connecting rod (6). The two-stroke engine includes several transfer channels (14), which, referred to a symmetry plane (49), lie on opposite sides (47, 48) with the plane partitioning approximately the outlet (10). The transfer channels (14) connect the crankcase (4) to the combustion chamber (3). A first end (20) of each transfer channel (14) opens via an entry window (12, 15) into the combustion chamber (3) and the second end (19) of each transfer channel opens to the crankcase (4). Each transfer channel (14) is connected, between its ends (19, 20), to an air channel (22a, 22b) via a membrane valve (21). Air is supplied by the air channel (22a, 22b) via an adjustable throttle (31, 32).