This is a method and an apparatus for the treatment or introduction of contrast fluids into tissue, particularly cardiac tissue. The apparatus includes a catheter having an elongated flexible body and a tissue infusion apparatus including a hollow infusion needle configured to secure the needle into the tissue when the needle is at least partially inserted into the tissue to help prevent inadvertent removal of the needle from the tissue. This permits the selected treatment or contrast fluid to be confined to a specific site. The catheter may also include a visualization assembly including a transducer at the distal end of the body.