A plate heat exchanger, comprising: a plurality of heat transfer plates, which are stacked on top of each other; and gaskets disposed in the gasket grooves of some of the plurality of heat transfer plates. where the heat transfer plates comprise: a plate body having a first side and a second side opposite to the first side; a gasket groove formed on the plate body, depressed from the plate body in a direction from the first side towards the second side, and having a bottom wall, the bottom wall having a bottom wall body; and an inlet opening formed in the plate body for forming an inlet port of the plate heat exchanger; and an outlet opening formed in the plate body for forming an outlet port of the plate heat exchanger, and: wherein the gasket groove includes at least one first segment and one second segment, the first segment being in an area around the inlet opening and the outlet opening, and the second segment extending in a direction from the inlet opening to said outlet openings along an edge portion of the plate body, where in the heat exchanger a gasket is disposed at only one side of the heat transfer plate in the first segment, while the other side is unsupported, where two recesses are formed on the first segment of the bottom wall body in a length direction of the bottom wall body respectively disposed on two sides (31, 32) of the first segment in a width direction of the first segment, and spaced from each other in the width direction of the first segment and depressed from the bottom wall body in the direction from the first side towards the second side, and extending along the first segment of the bottom wall body of the gasket groove, the plate heat exchanger being characterized in that: said second segment of the bottom wall body of the bottom wall is different from that of the first segment, wherein no recess is formed in the second segment bottom wall body of the bottom wall which is essentially flat. a plurality of heat transfer plates, which are stacked on top of each other; and gaskets disposed in the gasket grooves of some of the plurality of heat transfer plates. where the heat transfer plates comprise: a plate body having a first side and a second side opposite to the first side; a gasket groove formed on the plate body, depressed from the plate body in a direction from the first side towards the second side, and having a bottom wall, the bottom wall having a bottom wall body; and an inlet opening formed in the plate body for forming an inlet port of the plate heat exchanger; and an outlet opening formed in the plate body for forming an outlet port of the plate heat exchanger, and: wherein the gasket groove includes at least one first segment and one second segment, the first segment being in an area around the inlet opening and the outlet opening, and the second segment extending in a direction from the inlet opening to said outlet openings along an edge portion of the plate body, where in the heat exchanger a gasket is disposed at only one side of the heat transfer plate in the first segment, while the other side is unsupported, where two recesses are formed on the first segment of the bottom wall body in a length direction of the bottom wall body respectively disposed on two sides (31, 32) of the first segment in a width direction of the first segment, and spaced from each other in the width direction of the first segment and depressed from the bottom wall body in the direction from the first side towards the second side, and extending along the first segment of the bottom wall body of the gasket groove, the plate heat exchanger being characterized in that: said second segment of the bottom wall body of the bottom wall is different from that of the first segment, wherein no recess is formed in the second segment bottom wall body of the bottom wall which is essentially flat. a plate body having a first side and a second side opposite to the first side; a gasket groove formed on the plate body, depressed from the plate body in a direction from the first side towards the second side, and having a bottom wall, the bottom wall having a bottom wall body; and an inlet opening formed in the plate body for forming an inlet port of the plate heat exchanger; and an outlet opening formed in the plate body for forming an outlet port of the plate heat exchanger, and: wherein the gasket groove includes at least one first segment and one second segment, the first segment being in an area around the inlet opening and the outlet opening, and the second segment extending in a direction from the inlet opening to said outlet openings along an edge portion of the plate body, where in the heat exchanger a gasket is disposed at only one side of the heat transfer plate in the first segment, while the other side is unsupported, where two recesses are formed on the first segment of the bottom wall body in a length direction of the bottom wall body respectively disposed on two sides (31, 32) of the first segment in a width direction of the first segment, and spaced from each other in the width direction of the first segment and depressed from the bottom wall body in the direction from the first side towards the second side, and extending along the first segment of the bottom wall body of the gasket groove, the plate heat exchanger being characterized in that: said second segment of the bottom wall body of the bottom wall is different from that of the first segment, wherein no recess is formed in the second segment bottom wall body of the bottom wall which is essentially flat.