In a method for substantially isolating cardiac circulation from systemic circulation, flow between the coronary sinus and the right atrium is occluded. A venous collection device having a collection lumen and a support structure is located in the coronary sinus. The support structure is used to maintain patency of the coronary sinus during collection of fluid through the collection lumen. An artificial flow path is provided between the collection lumen and the one or more coronary arteries, thus isolating the cardiac circulation. According to the method, cardiac pumping for systemic circulation can be maintained during isolation of the cardiac circulation.