The present invention provides a compound of Formula I or a pharmaceutically acceptable salt thereof, wherein R1, R2, R3, A1, A2, A3, B1, B2, B3 and B4 are as defined herein. The compounds of Formula I have been found to act as glucagon antagonists or inverse agonists. Consequently, the compounds of Formula I and the pharmaceutical compositions thereof are useful for the treatment of diseases, disorders, or conditions mediated by glucagon.