Effects of pulsed microwave radiation on the contractile rate of isolated frog hearts.

Hearts from 81 frogs were divided into 10 groups and placed individually in a temperature-controlled waveguide filled with Ringer's solution. Hearts of Group A served as controls. Hearts of the other nine groups were treated with pulsed microwaves (2450 MHz, 10 microseconds, 100 pps) that ranged from a specific-absorption rate (SAR) of 2 to 200 W/kg. In several groups, an electrocardiogram was used to synchronize microwave irradiation with the heartbeat. In one group of frog hearts exposed at 200 W/kg, the heart rate slowed down sharply 25 minutes after irradiation, by which time the temperature of the Ringer's solution had risen by 7 degrees C. In another group exposed at 200 W/kg but under constant temperature, the heartbeat almost paralleled that of the control group. Other groups, including exposures of frog hearts to 16 Hz modulated CW or pulsed fields at SARs from 3 mW/kg to 8.55 W/kg, showed no effects of pulsed microwave irradiation on heartbeats; no brachycardia or tachycardia were found at constant temperatures.