Subject line for cold emails?

I have recently begun cold email outreach and am looking for suggestions for subject line headings. I have played around with
"introduction", "opportunity", Hi (insert name) and the name of industry i.e. "healthcare".

What have your experiences been with trying various subject line headings and what was the click through rate?
I have not seen the analytics to understand the effectiveness of the various subject lines, but it is on my to do list as I believe there is value in understanding what works and what doesn't. I am interested to learn how people are approaching this challenge. Thanks