The present invention relates generally to a device and method for preventing the undesired passage of emboli from a venous blood pool to an arterial blood pool. The invention relates especially to a device and method for treating certain cardiac defects, especially patent foramen ovales and other septal defects, through the use of an embolic filtering device capable of instantaneously deterring the passage of emboli from the moment of implantation. The device consists of a frame, and a braided mesh of sufficient dimensions to prevent passage of emboli through the mesh. The device is preferably composed of shape memory allow, such as nitinol, which conforms to the shape and dimension of the defect to be treated.