Heart valve allografts are widely used for surgical treatment of the heart. In recent years a new field of research has emerged dealing with allograft modification by cells of recipient by means of tissue engineering. This method involves culturing fibroblasts and endothelial cells, using recipient tissue, followed by introduction of the fibroblasts into tissues of allograft and coating its surface by the endothelial cells. This modification is expected to ensure the structural maintenance of implanted tissues and to reduce its thrombogenecity. This procedure may promote the allograft adhering to the recipient tissues, thus prolonging the terms of the valve normal functioning after implantations. For this purpose, methods of luminescent microscopy are suggested using double staining of tissue with fluorescent dyes Hoechst 33,342 and ethidium bromide, or with fluorescein diacetate and ethidium bromide. Experimental results are presented indicative of fibroblast migration from the surface to the human heart valve leaflets.