ECG/EKG

Just a quick one I had an ECG. A bout 3 months back and it checked out clear but because of my inability (most of the time ) to take a deep breath the last few days I'm scared its heart failur or something...if it was serious and not anxiety related would that ECG have picked something up 3 months ago...sure a heart disease or condition can't just pick up over 12 weeks! !? I'm driving myself crazy because I'm also getting popping feelings in my belly near my ribs and short bursts of pain in belly )"( I was diagnosed with constipation a couple of weeks ago)