To the Editor: —I read with interest the Inhaled Aerosol Symposium appearing in the January issue of theArchives of Internal Medicine. Of particular interest to me was Dr. Harris' summary of the cardio-toxic effects of aerosol propellants. I am concerned, however, that a body of experimental evidence with different emphasis has been overlooked. With constant, high-frequency tape recording from multiple intracardiac and extracardiac sites, dogs exposed in similar fashion to the human victims infrequently died, with cardiac mechanisms suggesting increased excitability or automaticity. Rather, there appeared to be a progressive, profound suppression of first the sinoatrial node and then successively lower pacemaker sites.1-3Even with careful and constant control of oxygen and carbon dioxide pressures, base excess, bicarbonate, and pH during entire experiments involving 30 dogs, death occurred in half, with evidence of progressive obliteration of one pacemaker site after another and ultimate electrical asystole. In two animals