Final answer:
A nurse should notify the provider immediately if they encounter dark, tarry stools in a client taking aspirin daily, as this can indicate a serious side effect like gastrointestinal bleeding or ulcers.
Step-by-step explanation:
A nurse who is assessing a client that has been taking aspirin daily for the past year should notify the provider immediately if they encounter a finding of dark, tarry stools.
Dark, tarry stools can indicate a serious side effect of aspirin usage such as gastrointestinal bleeding or ulcers, which is a result of aspirin's antiplatelet effects that can lead to increased bleeding times. Occasional bruising and heartburn are less immediately concerning side effects, although they still warrant monitoring, and a mild headache could be unrelated to the aspirin regimen. Given the potential risks associated with long-term aspirin use, particularly including increased risk of ulcers and gastrointestinal bleeding, these findings should be promptly communicated to the healthcare provider.