Hi KatyJoy. YES YES YES I know how frightening this can be. I had the same with Docetaxal. My shortness of breath was more concerning to me than the tachycardia. I ended up in emergency 3 times because I felt I couldn't breathe. They did ultrasounds of the heart, echos, xrays and took a CT scan three times to check for a blood clot on the lungs. One time when I had the attack they rang my husband at work and told him to get to the hospital immediately which scared the daylight out of him! In the end it all stopped after I finished docetaxal. I remember other women on the network having the same experience. I changed chemo oncologists during treatment. My second doctor said this was a side effect of dexamethasone taken with docetaxal and that he had seen before but only in a few women. Here's hoping it is just that and it will all settle down like mine did about 4 - 6 weeks after your last dose of docetaxal. Good luck with everything.