Myocytes from atria of adult guinea-pigs were isolated by means of a previously described enzyme perfusion with some modifications. The problem of Ca-intolerance of the dispersed cells was circumvented by (i) avoiding cooling of the cells below 25 degrees C and (ii) increasing the Ca concentration slowly already during the enzyme perfusion. Isolated atrial myocytes were taken in long-term cell culture. Under this condition they become spherical within about 2 days. The rounded stage (cardioballs), which is found in the cultures for a period of ca. 10 days is highly suited for electrophysiological studies using the different recording configurations of the patch clamp technique, including 'tight-seal whole-cell recording' with simultaneous cell dialysis.