Inotropic responses of isolated atrial and ventricular muscle from the dog heart to inosine, guanosine and adenosine.

1. The inotropic effects of inosine, adenosine and guanosine were compared in isolated and blood-perfused canine atrial and ventricular muscle preparations paced at 1.5-2.5 Hz. 2. In isolated atria, guanosine and inosine usually had positive inotropic effects, but adenosine consistently had a marked negative inotropic effect. 3. In ventricular muscles, the three purine compounds examined produced dose-related positive inotropic responses, but adenosine also produced a slight negative inotropic response which preceded the positive inotropic response.