We present an unusual case of an anomalous left coronary artery arising from the contralateral sinus of Valsalva: a 63-year-old male patient who consulted to our emergency department with 1-week history of progressive dyspnea on exertion with clinical signs of heart failure, associated with lung congestion on the chest X ray and elevated NT-proBNP levels (2000 pg/ml; normal value <150). Doppler echocardiography showed severe dilation of both left atrium and left ventricle, with severe deterioration of LV systolic function (Ejection fraction of 26%), global hypokinesia and a moderate mitral regurgitation with central jet. A cardiac catheterization was performed, which evidenced an anomalous origin of the left main coronary artery from the right coronary sinus with a proximal lesion of nearly 50%. A coronary computed tomographic angiography confirmed the diagnosis of an anomalous origin with an intramyocardial path at the level of the interventricular septum, associated with moderate extrinsic compression. To determine the degree of functional ischemia presented by the left main coronary artery lesion we performed a fractional flow reserve evaluation, resulting in 0.75, which was ranked as significant. An angioplasty with implantation of a drug-eluting stent (with Everolimus) was performed successfully to the target lesion. The patient evolved favorably during hospitalization and was discharged from the medical center to continue outpatient follow-up. Patient remained asymptomatic at 1-month and 6 months, during clinical evaluation, without evidence of ischemia on noninvasive functional assessment.