WordWeb Online

1. Marked by or paying little heed or attention
   "We have always known that heedless self-interest was bad morals; we know now that it is bad economics"; "heedless of danger"; "heedless of the child's crying"
   - unheeding
    
2. Characterized by careless unconcern
   "the heedless generosity and the spasmodic extravagance of persons used to large fortunes"
   - reckless

See also: attentiveness, careless, deaf, heed, heedlessly, heedlessness, indifferent, paying attention, regard, regardless

Antonym: heedful