Thyroid hormone acts on heart and peripheral vascular system in multiple ways. Most of the cardiac manifestations are reversible with adequate and timely thyroid therapy. Echocardiographic changes are present in patients with untreated hypothyroidism and the changes are reversible with treatment. Aim of the study was to evaluate the structural and functional changes of the heart in hypothyroid patients and its response to treatment. This prospective observational study was performed in the Bangabandhu Sheikh Mujib Medical University, Dhaka, Bangladesh from November 2012 to April 2013. The study included 35 cases and 35 control based on their thyroid hormonal status. The cases were previously untreated for hypothyroidism. By 2D and M-mode echocardiography LV septal wall and posterior wall thickness, LVIDD, LVIDS, LA and Aortic diameter and ejection fraction were measured. Mitral inflow pattern was observed through pulse wave Doppler and peak E velocity, a velocity and E/A ratio were noted. All the observations were noted both in cases and controls and in cases after normalization of hypothyroid status. Echocardiographic variables showed that septal wall and posterior wall thickness, LVIDD and LVIDS were higher in the cases than those in the control group. Left ventricular ejection fraction was lower in case group compared to control group. Of the mitral inflow parameters, a velocity was higher and E/A ratio lower in cases than those in control group. Following treatment of >3 months the septal wall and posterior wall thicknesses were reduced significantly (p<0.001 and p<0.001 respectively) and Left ventricular ejection fraction was also improved significantly (p<0.001) from its baseline status. Of the mitral inflow parameters, E-velocity was significantly increased, A-velocity significantly decreased and E/A ratio significantly increased from their baseline figures (p=0.016, p=0.032 and p<0.001 respectively). Cardiovascular complications of hypothyroidism increase the morbidity of the patients. Results of our study showed importance of early diagnosis and prompt treatment reversed the condition and that will diminish the extent of cardiac complications.