Male rats were exposed to 0, 10 and 130 p.p.m. cadmium administered in 0.5% saline drinking water for 71 days. Biweekly records of ECGs, Hct, body weight and blood levels of cadmium were made. Rats exposed to 130 p.p.m. cadmium showed slower growth rates and declining Hct indicative of acute cadmium poisoning. At the end of the experimental period, carotid artery blood pressures and whole heart cadmium levels were determined. Although no significant blood pressure changes were observed in the experimental groups, the cadmium content of the hearts of the higher dose group was significantly higher than in the hearts of the lower dose group. The PR interval of the ECG was lengthened progressively and to the same extent in both experimental groups with continued cadmium feeding. These experiments offer evidence that the accumulation of even moderate amounts of cadmium will be manifested in marked changes in cardiac conduction without overt signs of cadmium poisoning.