50 y/o woman. i recently started running. is it dangerous for me to run and elevate my heart rate over 143 bpm for extended periods?

How do you feel?: Your body usually gives you clues about its condition under stress. 120 - 144 is about the level you should be - that is 70% - 85% of your maximum predicted heart rate - as long as you have no symptoms. Check with your doctor if you have other medical issues or a history that might require modification of this level of exercise. Enjoy!