What Causes Heart Palpitation And Swollen Foot/ankle?

Heart palpitates and catches my breath but almost always leads into a migraine after. Lately they have been getting extremely more frequent. Also last week my left foot and ankle swelled and I felt it travel to my knee. Went to the hospital er and they did an xray and ultrasound to see if there was a blood clot. Nothing in my foot to leg and it took over two days for it to decrease in size. I have one kidney.