Significant complications of the operation include bleeding, heart problems (heart attack, arrhythmias), stroke, infections (often pneumonia) and injury to the kidneys. Uses
Coronary artery bypass surgery aims to prevent death from coronary artery disease and improve quality of life by relieving angina. Indications for surgery are based on studies examining the pros and cons of CABG in various subgroups of patients (depending on the anatomy of the lesions or how well heart is functioning) with CAD and comparing it with other therapeutic strategies, most importantly percutaneous coronary intervention (PCI). Coronary artery disease
Coronary artery disease  is caused when coronary arteries of the heart accumulate atheromatic plaques, causing stenosis in one or more arteries and place myocardium at risk of myocardial infarction. CAD can occurs in any of the major vessels of coronary circulation, which are Left Main Stem, Left Ascending Artery, Circumflex artery, and Right Coronary Artery and their branches. CAD can be asymptomatic for some time- causing no trouble, can produce chest pain when patient is exercising, or can produce angina even at rest. The former is called stable angina, while the latter unstable angina. Worse, it can manifest as a myocardial infarction, in (which the blood flow to a part of myocardium is blocked. If the blood flow is not restored within a few hours, either spontaneously or by medical intervention, the specific part of the myocardium becomes necrotic (dies) and is replaced by a scar.
It has also been noted that the timing of the operation, plays a role in survival, it is preferable to delay the surgery if possible (6 hours in cases of nontransmural MI, 3 days in cases of transmural MI)CABG of coronary lesions is also indicated in mechanical complications of an infarction (ventricular septal defect, papillary muscle rupture or myocardial rupture) should be addressed There are no absolute contraindications of CABG but severe disease of other organs such as liver or brain, limited life expectancy, fragility should be taken into consideration when planning the treatment path of a patient. Other cardiac surgery
CABG is also performed when a patient is to undergo another cardiac surgical procedure, most commonly for valve disease, and at angiography a significant lesion of the coronaries is found. CABG can be employed in other situations other than atheromatic disease of native heart arteries, like for the dissection of coronary arteries (where a rupture of the coronary layers creates a pseudo-lumen and diminishes blood delivery to the heart) caused e.g. by pregnancy, tissue diseases as Enhler-Danlos, Marfan Syndrome, cocaine abuse or Percutaneous Coronary Intervention). A coronary aneurysm is another reason for CABG, for a thrombus might develop within the vessel, and  possibly travel further. CABG vs PCI
CABG and percutaneous coronary intervention (PCI) are the two modalities the medical community has to revascularize stenotic lesions of the cardiac arteries.