An improved method for isolating cardiac myocytes is described. This method consists of the initial dispersion of the myocytes with a new type of collagenase and the following treatment of the cells with a non-specific protease. This method gives more than 80% rod-shaped, viable, and quiescent cells, which are suitable for biochemical as well as electrophysiological experiments. Formation of a G omega seal and subsequent whole-cell recording is easily performed using these cells.