I had an 24 hr ecg and at a time i was walking at a normal pace my heart rate was 180bpm and i was feeling breathless it was in sinus rhythm causes?

?: This might be normal for you, the heart rate response I mean to exercise. Alternately it could be you need more aerobic exercise

Sinus Tachycardia: Many reason for rapid heart rate: i.e. Atrial Fibrilation, Flutter, PSVT, Sinus Tachycardia. If it is Sinus Tachycardia asyou mentioned, the causes are as below: Hyperthyroidism, fever, volume depletion, anxiety, pheochromocytoma, sepsis, anemia, hypotension and shock, pulmonary embolism, heart failure, low oxygen, COPD, nicotine or caffeine etc....