Recently my heart has been pounding very hard immediately after standing. I am a 43 yr old man that smokes and drinks, but not heavily. I did have some anxiety from stress several months ago, but this heart pounding is not the same symptoms. I have trouble catching my breath, it feels like my heart is racing, but it isn t really, just pounding through my chest and throat. I typically can make it feel better by taking deep breaths. I was wondering if it is a lack of oxygen in my blood? Maybe not resting fully. But they I noticed below that tachycardia may be the cause? I have had ECG s and have worn a heart monitor and there is nothing seemingly wrong with my ticker. I can also almost feel when it is going to happen as my legs feel like i just ran a sprint. My quads ache like they are full of latic acid. Any suggestions? Thank you