A perfusion system comprising: an oxygenator for oxygenating blood for delivery to a patient; a first pump for pumping blood towards the oxygenator; and a cardioplegic agent delivery system, wherein the cardioplegic agent delivery system comprises: a supply reservoir (10; 40; 60) for a carrier fluid for the cardioplegic agent, a delivery channel for the carrier fluid, the delivery channel leading from the supply reservoir (10; 40; 60) to an outlet of the delivery channel supplying a cardioplegic line, and a second pump configured to i) effect a flow of the carrier fluid in the delivery channel from the supply reservoir (10; 40; 60) to the outlet above a minimum driving pressure for the delivery of cardioplegic agent, and, ii) to render the carrier fluid in a condition suitable for the administration of cardioplegic agent, wherein the supply reservoir (10; 40; 60) is configured to hold carrier fluid below the minimum driving pressure, the second pump is a centrifugal pump configured to receive carrier fluid from the supply reservoir (10; 40; 60) at a pressure below the minimum driving pressure and to effect a flow of the carrier fluid to the outlet at a flow rate and above the minimum driving pressure for the delivery of cardioplegic agent, and the cardioplegic agent delivery system comprises a flow sensor for sensing the flow of the carrier fluid downstream of the centrifugal pump. an oxygenator for oxygenating blood for delivery to a patient; a first pump for pumping blood towards the oxygenator; and a cardioplegic agent delivery system, wherein the cardioplegic agent delivery system comprises: a supply reservoir (10; 40; 60) for a carrier fluid for the cardioplegic agent, a delivery channel for the carrier fluid, the delivery channel leading from the supply reservoir (10; 40; 60) to an outlet of the delivery channel supplying a cardioplegic line, and a second pump configured to i) effect a flow of the carrier fluid in the delivery channel from the supply reservoir (10; 40; 60) to the outlet above a minimum driving pressure for the delivery of cardioplegic agent, and, ii) to render the carrier fluid in a condition suitable for the administration of cardioplegic agent, wherein a supply reservoir (10; 40; 60) for a carrier fluid for the cardioplegic agent, a delivery channel for the carrier fluid, the delivery channel leading from the supply reservoir (10; 40; 60) to an outlet of the delivery channel supplying a cardioplegic line, and a second pump configured to i) effect a flow of the carrier fluid in the delivery channel from the supply reservoir (10; 40; 60) to the outlet above a minimum driving pressure for the delivery of cardioplegic agent, and, ii) to render the carrier fluid in a condition suitable for the administration of cardioplegic agent, wherein the supply reservoir (10; 40; 60) is configured to hold carrier fluid below the minimum driving pressure, the second pump is a centrifugal pump configured to receive carrier fluid from the supply reservoir (10; 40; 60) at a pressure below the minimum driving pressure and to effect a flow of the carrier fluid to the outlet at a flow rate and above the minimum driving pressure for the delivery of cardioplegic agent, and the cardioplegic agent delivery system comprises a flow sensor for sensing the flow of the carrier fluid downstream of the centrifugal pump.