WordWeb Online

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

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

Antonym: thoughtful