The article presents a case of subacute coronary artery thrombosis investigated by classic methods, coronary angiography, and MRI. T1- and T2-weighted images showed high signal intensity within the lumen of the right coronary artery corresponding to the methemoglobin content of the thrombus. Dynamic sequence images with intravenous gadolinium contrast agent displayed lack of right coronary artery enhancement, confirming coronary occlusion. The coronarography revealed the same finding. MRI appears to be a promising method of coronary thrombosis assessment.