Martinez is expected to undergo a Villa medical in Birmingham today.
The Birmingham Mail says Heaton was surprised to learn of Villa's all-out pursuit to bring in a new No.1 with Dean Smith not prepared to gamble on Jed Steer, Orjan Nyland or Lovre Kalinic ahead of Sheffield United.
Heaton, 34, remains sidelined until late October at the earliest and doubts remains as to whether he can return to the form he showed prior to his cruciate tear on January 1. By the time Heaton's ready for a return he'd have been out for almost 11 months, hence the reason why Smith and Villa have been so keen to get Martinez in from Arsenal.
The reason why Martinez stood out was his form, Premier League know-how and availability. Villa are paying £20m to sign the Argentine.