A blood pump, comprising: - a pump casing having a blood flow inlet and a blood flow outlet connected by a passage, and - an impeller arranged in said pump casing so as to be rotatable about an axis of rotation, the impeller being provided with blades sized and shaped for conveying blood along the passage from the blood flow inlet to the blood flow outlet, the impeller being rotatably supported in the pump casing by at least one bearing (10, 20), wherein a surface of the impeller faces a surface of the pump casing spaced from said surface of the impeller by a clearance, the clearance being in fluid connection with the passage at a clearance transition point, wherein at least one wash out channel extends through the impeller and is in fluid connection with the passage via a first opening and with the clearance via a second opening, wherein the first opening of the wash out channel is arranged in an area of the impeller that - during operation of the blood pump - is under a higher pressure than the clearance transition point so as to cause a blood flow from the first opening through the wash out channel and the clearance to the clearance transition point, characterized in that a protrusion extends into the first opening of the wash out channel and is sized and shaped to increase a blood flow through the first opening into the wash out channel, and/or the impeller comprises at least one wing extending radially therefrom and being disposed adjacent to and behind the first opening of the wash out channel with respect to the direction of rotation. - a pump casing having a blood flow inlet and a blood flow outlet connected by a passage, and - an impeller arranged in said pump casing so as to be rotatable about an axis of rotation, the impeller being provided with blades sized and shaped for conveying blood along the passage from the blood flow inlet to the blood flow outlet, the impeller being rotatably supported in the pump casing by at least one bearing (10, 20), wherein a surface of the impeller faces a surface of the pump casing spaced from said surface of the impeller by a clearance, the clearance being in fluid connection with the passage at a clearance transition point, wherein at least one wash out channel extends through the impeller and is in fluid connection with the passage via a first opening and with the clearance via a second opening, wherein the first opening of the wash out channel is arranged in an area of the impeller that - during operation of the blood pump - is under a higher pressure than the clearance transition point so as to cause a blood flow from the first opening through the wash out channel and the clearance to the clearance transition point, characterized in that a protrusion extends into the first opening of the wash out channel and is sized and shaped to increase a blood flow through the first opening into the wash out channel, and/or the impeller comprises at least one wing extending radially therefrom and being disposed adjacent to and behind the first opening of the wash out channel with respect to the direction of rotation. wherein a surface of the impeller faces a surface of the pump casing spaced from said surface of the impeller by a clearance, the clearance being in fluid connection with the passage at a clearance transition point, wherein at least one wash out channel extends through the impeller and is in fluid connection with the passage via a first opening and with the clearance via a second opening, wherein the first opening of the wash out channel is arranged in an area of the impeller that - during operation of the blood pump - is under a higher pressure than the clearance transition point so as to cause a blood flow from the first opening through the wash out channel and the clearance to the clearance transition point, characterized in that a protrusion extends into the first opening of the wash out channel and is sized and shaped to increase a blood flow through the first opening into the wash out channel, and/or the impeller comprises at least one wing extending radially therefrom and being disposed adjacent to and behind the first opening of the wash out channel with respect to the direction of rotation.