Example of transthoracic Doppler findings of collateral blood flow in the apical region, compared with coronary angiography. (A) In a modified parasternal long-axis view focusing on the apex and distal anterior interventricular sulcus, several epicardial and intramyocardial collaterals (CL) originates from the distal left anterior descending coronary artery (dLAD). (B) Angiogram of the left coronary artery demonstrates apically located epicardial and intramyocardial collateral (CL) blood supply from the dLAD to the posterior descending coronary artery (PDA), which shows retrograde flow. Angiogram of the right coronary artery demonstrated a proximal PDA occlusion (not shown). LAD = left anterior descending coronary artery, LV = left ventricle, RV = right ventricle.