Answer:
Immobilize his arm and positioning it below heart level.
Explanation:
Based on the information provided within the question it can be said that in this scenario you should Immobilize his arm and positioning it below heart level. This seems to be the general consensus and guideline from the University of Arizona poison and drug information center. You must not apply a tourniquet or anything else that may prevent blood-flow. Rattlesnake bites are rarely fatal if treated.