Hi there. If you are serious about evaluating your heart including its rhythm, you should attend your doctor or a medical professional to check it out. Recording it is not really much use, its a waste of time
I agree, a stethoscope doesn't seem to be the right way. But I bought an AliveCor ECG monitor that you attach to your phone - if nothing else, at least it gives you a good indication of what your heart rythm is and go from there. There is a new one out now called "Preventicus Heartbeat" that works entirely in software, but you need an Iphone - don't know what version - or an Android phone with version 5 or 6 which I don't have, so I haven't tried it yet.