I am a female. 49 years old. Been running the last 4 months. Started doing 2/1 intervals. Run in zone 2 minutes walk 1 minute and on for 30 minutes. At the end I ran hard and my chest began to tighten. Heart rate was 166. When I stopped it went away. Ran

Likely odd. If only one time , then probably an oddity. You should be watching your heart rate monitor. Be sure you are properly recovered each set. Should only do these 1 x week. Mix easy distance in with the week's plan. What is the goal and your background ? may ask running club for advice, or coach. Good luck. (USAT Level I certified coach)
Hmmm. Not knowing anything more bout you, is hard to be specific. Assuming you r a healthy 49 y/o woman on no meds for chronic diseases, non smoker, no family hx of premature heart disease, it is unlikely that this represents heart disease, BUT, w/ a symptom of chest tightness, at this high high rate u shud see your doc to be evaluated, & have a regular stress test pushing to u to your max heart rate.
See your PCP. Your physician can help you identify the cause of any chest pain. If you have pain or discomfort in your chest, neck, jaw or arms during physical activity, see your PCP.