hello Anna,
Above all else, you should at least talk to your doctor about what happened. In the meantime, I can at least tell you a few things. You said you were having a severe constipation episode; when a person strains he is giving himself what is called a Valsalva response in the body. For a few seconds the heart stops beating and then when it resumes, sometimes you will feel strong heartbeats, sometimes the rate will be a bit faster than normal until it regulates itself back to the norm. These are perfectly normal responses, in fact, the Valsalva is actually USED to create a normal heart beat in patients who have certain types of fast heart beats such as in patients with supraventricular tachycardia! Right after straining, sometimes even during, you feel faint because for that brief period, the brain lacks blood flow. It sounds like the straining you were doing irritated your chest and back muscles as well. You don't give your age on here, but say you have a young child so there is more good news. It's VERY rare for a young woman to have a heart attack because she is pretty much protected from that problem during child bearing years, for that reason alone. Her heart has to be able to take care of the baby she is carrying as well as to go through the pressures of labor. Also, a person has to eat junk food for a period of twenty years BEFORE there is enough blockage I the arteries of the heart to cause heart attacks. There are some forms of cardiomyopathies that can lead to heart attacks because of a lack of blood flow down through the heart muscle, but if that was the case, you would have been well aware of that before now, for sure. See your doctor and try not to live on MedHelp for all the answers. There are a lot of knowledgeable members on here who speak from personal experience, but everyone is different so, as I said before, ask to see your doctor about all of this. Take care