The cooling fluid (1) is designed to be introduced into the pericardium (3) of the heart (2) and contains either a crystalloid or a crystalloid with substances neutralizing harmful products of oxygen metabolism. In another version the cooling fluid (1) contains a dose of antiarrhythmic drug. The heart (2) is cooled down directly by the cooling fluid (1) introduced by a pericardial catheter (4) via cooling ducts (5) into the pericardium (3). The amount of cooling fluid (1) introduced in and withdrawn from the pericardium (3) as well as its temperature and pressure inside the pericardium (3) is monitored. The temperature in the pericardium (3) is regulated depending on the clinical requirements in the rage from 10°C to 36°C. The subject of the invention is also another device (11), pericardial catheter (4) and another cooling fluid and its use which enables maintaining the temperature in the range from 10°C to 36°C inside the pericardium (3) during the cardiac hypothermia (2). The invention is used for a direct cardiac hypothermia (2) in case of cardiac arrest (2), arrhythmia and whenever it is necessary to decrease the oxygen metabolism of cardiac tissue (2), for example in the case of bridging, in advanced coronary artery disease (2), in heart transplantation (2), and can be used as cardioprotection in procedures such as TAVI and BAV, etc.L'invention concerne un fluide de refroidissement (1) qui est conçu pour être introduit dans le péricarde (3) du cœur (2) et qui contient un cristalloïde ou un cristalloïde comportant des substances neutralisant les produits nocifs du métabolisme de l'oxygène. Selon une autre version, le fluide de refroidissement (1) contient une dose de médicament anti-arythmisant. Le cœur (2) est refroidi directement par le fluide de refroidissement (1) introduit par un cathéter péricardique (4) par des conduites de refroidissement (5) dans le péricarde (3). La quantité de fluide de refroidissement (1) introduit et retiré dans le péricarde (3) ai
