newly diagnose stage III

Hey everyone, My dad has just been diagnosed with stage III colorectal cancer.  The doctor removed 30% of his large intestine and a "large portion" of his small intestine.  The doc/surgeon/onc said that of the 42 "samples" he took 6 came back as stage III.  The other samples were fine.  I am confused.  Granted I am getting this third hand from my mother and I live far away so I am not able to be there during any of these discussions.  I was under the impression through internet searching that stage three meant the cancer had spread beyond the musculature and into surrounding organs or lymph nodes.  His doctor had said he removed the entire mass and it was contained within the musculature of his intestine.  My dad originally went into the hospital for atrial fib-he's had it for quite a while- he felt "off" and went to the e.r.  They were not able to regulate his heart until 3 days into being at the hospital his heart stopped for 7 seconds, he passed out and they then decided to put a pacemaker in.  He had complained of a persistent pain in his side so they CAT scanned it and found a mass.  He had the colonoscopy then the surgery to resect the tumor.  His doctor has suggested that after recovery from the pacemaker surgery and resect that he should start "aggressive treatment" right away.  What kind of treatment is my dad looking at, how long may it last and what should my family and I expect.  He is 77 and in otherwise good health.  Thanks for any advice/info.