WordWeb Online

1. Taking heed; giving close and thoughtful attention
   "heedful of the warnings"; "so heedful a writer"; "heedful of what they were doing";
   - attentive, thoughtful, paying attention
    
2. Cautiously attentive
   "heedful of his father's advice";
   - careful
    
3. Giving attention
   - advertent

See also: attentive, attentiveness, aware, heed, mindful, paying attention, regard

Antonym: heedless