The intraaortic balloon pump has been shown to decrease myocardial oxygen demand by afterload reduction, while increasing myocardial oxygen supply by diastolic augmentation of coronary blood flow. This diastolic augmentation of coronary flow has been demonstrated experimentally with invasive methods. Noninvasively, transesophageal echocardiography has demonstrated efficacy in enabling visualization of the proximal left coronary artery and in recording coronary blood flow velocity. To assess the potential of this technique in demonstrating quantitatively the increase in coronary flow during counterpulsation, 6 patients were studied during intermittent balloon pumping. Peak diastolic coronary blood flow velocity increased by a mean of 117% (range 62 to 287) during balloon inflation (p = 0.002). Furthermore, coronary flow velocity integral increased by a mean of 87% (range 43 to 176; p = 0.003). Problems associated with intraaortic balloon pumping were discovered by transesophageal echocardiography in 4 patients (incorrect balloon placement, damage to the aortic wall [2 patients], and premature balloon deflation time). Transesophageal echocardiography can be used in evaluating intraaortic balloon positioning within the aorta and in monitoring coronary artery flow augmentation during counterpulsation. This relatively noninvasive technique adds another dimension to the evaluation of balloon function and may help in optimizing the benefits of counterpulsation.