B737-700
Flight Crew Air Transport Pilot (ATP)
Distraction; Workload
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Rejected Takeoff
Human Factors
Conducted low speed rejected takeoff due to Master Caution Light.  Discovered the Pitot Probe Heat switches were off.  Redid the After Start; Taxi; and Takeoff checklists.  Notified Dispatch and departed. After push back; I elected to do the Delayed Engine [Start] Checklist and taxi out single engine.  The First Officer started the #2 engine and I called for the After Start checklist; while the push crew was still connected. Activity outside the aircraft by the push crew redirected my attention away from the checklist and I missed getting the Pitot Probe switches on.  My decision to call for the After-Start Checklist while I was monitoring the push back was a contributing factor; as well as workload distribution and cross verification.
B737-700 Captain reports forgetting to turn on the pitot heat switches after engine start and responding without checking at the checklist prompt. As takeoff thrust is set a Master Caution Light illuminates due to the omission; and the takeoff is rejected.