High Heart Rate causes and treatments?

I am a 40 years older male who had always lived fit and fine life but these days life is something that is full of trouble. Lately I have been fighting with high heart rate that has made my life go upside down in a few days. Can somebody elaborate me causes of High Heart Rate?  I wish to know of some measures for this High Heart Rate to be taken care of. Are these treatments reliable and effective. Waiting for your quick replies.