Absence of blocking effect of quinidine on responses to norepinephrine in the isolated dog atrium.

The isolated right dog atrium was perfused through the sinus node artery with blood led from a heparinized support dog under constant perfusion pressure of 100 mmHg. The positive chronotropic and inotropic responses to norepinephrine were not significantly suppressed by treatment with large amounts of quinidine or procainamide, but completely blocked by propranolol. From these results, it was demonstrated that quinidine and procainamide have no adrenergic beta-blocking activity on chronotropism and on inotropism in the heart.