The effects of continuous and amplitude-modulated radiofrequency electromagnetic waves on calcium efflux from 45 Ca preloaded frog hearts were examined. Frog hearts, electrically stimulated at their natural beating frequency, were exposed for 30 min to 240 MHz radiowaves in a Crawford irradiation cell. Exposures at incident power levels of 0.5, 0.8, 1.0, 1.2, 5.0 and 10.0 Watts (corresponding to calculated specific absorption rates (SAR) of 0.15, 0.24, 0.30, 0.36, 1.50, and 3.00 mW/kg) were tested either in the continuous wave mode or using sinusoidal amplitude modulation at 0.5 Hz, the average beating frequency of the frog hearts, or at 16 Hz. Continuous at 0.5 Hz amplitude-modulated waves did not affect calcium efflux from the hearts. However, 16 Hz amplitude-modulated electromagnetic radiation resulted in statistically significant increases in calcium efflux. The effect was most significant at the 1 W incident power level (17.9%, p<0.01) but was also observed at 0.5 W(21.0%, p<0.05). Therefore, it appears that frog hearts are affected by electromagnetic radiation at particular power levels and 16 Hz modulation frequency, a bioelectromagnetic interaction displaying power and frequency windows comparable to those reported by other investigators in calcium efflux studies on neural tissue.