42 CFR §424.124

1. (a)Basic rules. Medicare Part B pays for physician and ambulance services if—
   1. (1)They are furnished—
      1. (i)To an individual who is entitled to Part B benefits; and
      2. (ii)In connection with covered inpatient hospital services; and
   2. (2)They meet the conditions set forth in paragraphs (b) and (c) of this section.
2. (b)Physician services.
   1. (1)The physician services are services covered under Medicare Part B and are furnished—
      1. (i)In the hospital, during a period of covered inpatient services; or
      2. (ii)Outside the hospital, on the day of admission and for the same condition that required inpatient admission; and
   2. (2)The physician is legally authorized to practice in the country where he or she furnishes the services.
3. (c)Ambulance services. The ambulance services are—
   1. (1)Necessary because the use of other means of transportation is contraindicated by the beneficiary's condition; and
   2. (2)Furnished by an ambulance that meets the definition in § 410.41 of this chapter.