Meanings
Usage patterns
脈が速いfor one's pulse to be fast
After exercising, one's pulse becomes fast.
脈が乱れるfor the pulse to become irregular
The pulse can become irregular when one is nervous.
脈がないto have no hope or chance (of success)
I confessed to him, but it seems there's no chance.
Expressions
脈があるhave a pulse; be alive · have a chance; not altogether hopeless