Im always having tachicardia and i feel weak sometimes feel pain bellow back can it weaker heart? im 28 years old could it be heart failure or its cardiac aniexhy as kardiolog said ?

Tachycardia is documented by EKG . Heart rate more than 90 is tachycardia. If concerned - get a 3 day Holter for rate &rhythm. It is not uncommon to have an episode or two short burst of tachycardia in anyone over several days. Palpitations are irregular heart beats which will be noted. Doubt heart failure . Check thyroid function get EKG and 3 day holter (will reassure) F/u w./ MD

At your age, 28. Anxiety is probably more likely. However, never dismiss these symptoms. Younger people can definitely have arrhythmia's (Abnormal heart beat/or rate), and can have other forms of heart disease as well. I don't have enough information to give you a definitive answer. You should talk with your primary care doctor and ask if they feel you should be evaluated by a cardiologist.