Respiratory effects of acute coronary embolism were studied in mongrel dogs. Coronary embolism was produced by Agress's method and respirtory effects were observed for two hours. In the experimental group, in which coronary embolism was produced, there were relative decreases in respiratory rate and arterial oxygen saturation along with relative increases in tidal volume, minute ventilation, ventilation equivalent and arteriovenous oxygen difference compared to those in the control group. However, differences in these various measurements between tow groups, those in tidal volume and arterial oxygen saturation, have greatly diminished in two hours. These facts suggest that changes in respiratory rate, minute ventilation, ventilation equivalent and arteriovenous oxygen difference in the experimental group are early but short-lasting responses to acute coronary embolism, whereas changes in tidal volume and arterial oxygen saturation occur early and last longer.