A two-stroke internal combustion heat engine with fuel injection; the heat engine comprises: at least one cylinder, which comprises, on the inside, a combustion chamber; a piston, which is mounted inside the cylinder so as to slide in a reciprocating manner; a cylinder head, which closes the combustion chamber at the top and has a lower wall; a crankcase, from which the cylinder projects and in which a crank chamber is obtained; a crankshaft, which is housed in the crank chamber; a connecting rod, which connects the piston to the crankshaft; a spark plug, which is mounted through the cylinder head; an intake duct, which feeds fresh air towards the combustion chamber; a reed valve, which is arranged inside the intake duct and comprises: a wedge-shaped support body having two inclined outer walls, which are opposite one another and have an opposite inclination relative to one another, at least two first openings for the air taken in, which are made in the outer walls, and two first flexible reed petals, which closes the first openings; and an injector, which is provided with an injection nozzle through which fuel is injected towards the combustion chamber, is mounted through the support body of the reed valve and beside the first opening engaged by the first flexible reed petal, so that the injection nozzle is arranged on the outside of the support body, is not covered by the first flexible reed petal, and sprays fuel downstream of the reed valve relative to the fresh air feeding direction along the intake duct; the heat engine is characterized in that the injector is arranged between the two outer walls of the wedge-shaped support body. at least one cylinder, which comprises, on the inside, a combustion chamber; a piston, which is mounted inside the cylinder so as to slide in a reciprocating manner; a cylinder head, which closes the combustion chamber at the top and has a lower wall; a crankcase, from which the cylinder projects and in which a crank chamber is obtained; a crankshaft, which is housed in the crank chamber; a connecting rod, which connects the piston to the crankshaft; a spark plug, which is mounted through the cylinder head; an intake duct, which feeds fresh air towards the combustion chamber; a reed valve, which is arranged inside the intake duct and comprises: a wedge-shaped support body having two inclined outer walls, which are opposite one another and have an opposite inclination relative to one another, at least two first openings for the air taken in, which are made in the outer walls, and two first flexible reed petals, which closes the first openings; and an injector, which is provided with an injection nozzle through which fuel is injected towards the combustion chamber, is mounted through the support body of the reed valve and beside the first opening engaged by the first flexible reed petal, so that the injection nozzle is arranged on the outside of the support body, is not covered by the first flexible reed petal, and sprays fuel downstream of the reed valve relative to the fresh air feeding direction along the intake duct; the heat engine is characterized in that the injector is arranged between the two outer walls of the wedge-shaped support body.