I am a 25 years old female. I ve been dealing with tachycardia for the past two years. I had several ecgs done, 24 hours Holter monitoring, and echocardiography which ruled out any heart condition. The diagnosis is not clear, medics talk about pure tachycardia. My resting rate is constantly 90-115 bpm. It spikes up to 130-140 during my walks. Cardiologist prescribed me ivabradine 5mg/2 times a day. I ve been taking it for 5 days and heart rate has lowered at around 75 resting rate on average, which is good. However, I stopped taking it because I started having this horrible feeling of breathlessness, dyspnea, mainly at rest. What could cause it? Is it possible in any way that I am not used to needing less hair hence the dyspnea? I am used to palpitations and high rate so, I feel like I could live with it; question is, can I live with it? If so, should I limit physical activity in any way? What long term effects does it have on a sane heart? I don t take any other medication, except for an iron supplement. Thanks in advance.