How can you distinguish transient ischemic attack from a cva?  

A warning. A tia, change in function of a part of the body due to loss of blood supply in the brain lasting less than a day, is a warning of more serious problems that might arise in the near future. You should quickly visit your doctor or a neurologist, discuss the symptoms and then a decision can be made about study of the source of the TIA and proper therapy.
Not until later. Tia is transient, the neurol deficit resolves within about 24h. Cva leaves more permanent (albeit somewhat reversible) damage. Tia is a warning sign for stroke. Stroke (cva) is brain attack (akin to heart attack). Sudden symptoms: change in consciousness, speech, strength, sensation, need to be evaluated emergently. Time is brain. Get checked immediately; if cva, may get rx with clot buster meds.
TIA better w/in 24h. The symptoms of transient ischemic attack (TIA) and cva (stroke) are indistinguishable. By definition, a TIA completely resolves within 24 hours.