A little older than who you are asking for replies from, but wanted to share just in case. This might be long, so I will put a tldr at the bottom. So I woke up one morning and went to work. About 11AM my chest started hurting. The pain wouldn’t go away, and even tried baby aspirin. My fear of needles caused me to seriously contemplate going to the hospital, but I decided I better, since this was a lot of pain. Went to the hospital and yes, I was having a heart attack. They shipped me off to a larger hospital where I had two stents placed the next morning. Was sent home a few days after that with meds. I had no meds, no aches, no pains until the actual event. Now I had a small list of prescriptions, a few new doctors, and had to recover. So I start on my new meds, one of which is a blood thinner, which my new cardiologist explains that "I don’t care if you stop taking everything else, but whatever you do, for the next year take the blood thinner religiously because if you don’t, those stents will clog up, and you may or may not make it back to the hospital when it happens. So with that in mind, I started my new life with meds. A couple of days into this, I had a very frightening experience. First real bowel movement after everything was getting back to normal, and it looked like a crime scene. It wasn’t like, is that blood, it was very apparent that I was bleeding. So I of course gave it a day or two, and nothing was changing. It was bad. So I called my cardiologist, and explained the what was going on. First thing he did was swap my blood thinner with another one. Then he let my primary doctor know. I switched blood thinners and that seemed to have stopped the blood, or at least from what it looked like. My primary doctor called and I explained what had happened and he put in a referral to a gastro doc. Now they couldn’t squeeze me in for a few months.

At this point things seem to have settled and I am doing cardio rehab but still haven’t seen a gastro doc. Since I wasn’t noticing blood in my stools I figured things were fine. About a month later I have a followup blood draw, and the next day I am coming back from cardio rehab and my primary care doctor calls me on the phone and asks if I am sitting down. I said I was driving, and he said he wasn’t even comfortable with me standing up. I told him I was a few mins from home and to call me back. He calls back when I got home and explained that my hemoglobin level was a 7, and that he wanted me to go to the emergency room for a transfusion right away. Get someone to drive me, and get it done. So another panic moment in my life where I almost said no due to my fear of needles, but I decided to go. To shorten this up a little, I went in and had a blood transfusion, and at this point they saw the urgency and that I was losing blood. So in that visit, I had an endoscopy and then a colonoscopy. To my shock I woke up from the colonoscopy to a doctor basically bluntly saying, I have bad news, you have colon cancer, and handing me a set of photos that you really don’t need to be a doctor to see that something is very wrong.

I spent a month waiting for surgery and to find out how bad things were. It was the longest month of my life, waiting and pondering how this was going to turn out. Just in case I started getting my affairs in order, etc. I ended up having surgery where they removed a section of my large intestine (colon) and a bunch of lymph nodes. After a week or so I got the results. Definitely cancer, but they had removed it all and it had not spread to the lymph nodes, which garnered me a diagnosis of Stage 2.

My point to this whole post is that in my case I had no symptoms that I could tell, and that’s scary as hell to me. I did find that there is a blood test that my oncologist did before and after, and it did show that something was wrong. But I believe that was only ordered because at that point we had the colonoscopy diagnosis and were waiting for surgery. There is no history of cancer in my family, and I have the dubious distinction of being the first. No symptoms that I can say, and if you had asked me the day before my heart attack how I felt, I would have probably told you that I was in the best shape I had been in years.

TLDR: Had a heart attack, which led to blood thinners causing me to bleed internally. This triggered a colonoscopy which found colon cancer. Surgery was all I needed luckily. Doing much better now, but to answer OP’s question, I had no symptoms or signs until my heart attack, which scares the hell out of me. So a heart attack basically saved my life.