Hello Jagriti, thanks for giving us an opportunity to solve your doubts. Diabetes is one of the biggest risk factors for ischemic heart disease which can be colloquially called as blockage in the vessels supplying the heart. With increasing age, hypertension, smoking, hyperlipidemia, the risk further increases. A positive TMT means your father is having Angina pectoris caused due to blockage of the coronary vessels. A nuclear stress test like a thallium scan is more specific and sensitive than TMT for reliably identifying the problem and the area of decreased regional blood flow. However, it cannot reliably determine the percentage of blockage. To determine the precentage of blockage, you will need an angiography or a noninvasive test like Cardiac MR or CT angiography.