OBJECTIVES: We evaluated the coronary vasodilatory effects of transcutaneous low-frequency (27-kHz) ultrasound (USD). BACKGROUND: Ultrasound has been shown to affect vascular function. METHODS: Ultrasound energy was administered transcutaneously to 12 dogs. Coronary arterial dimensions were assessed using intravascular coronary ultrasound (IVUS) and quantitative coronary angiography (QCA). RESULTS: The IVUS mid-left anterior descending (LAD) luminal area was 6.77 ± 1.27 mm2 at baseline. After 30 s of ultrasound, this area increased by 9% (7.40 ± 1.44 mm2, p < 0.05), after 3 min by 19% (8.05 ± 1.72 mm2, p < 0.05) and after 5 min increased by 21% (8.16 ± 1.29 mm2, p < 0.05). The mean coronary diameter (2.69 ± 0.33 mm) at baseline (QCA of three segments of LAD and three segments of left circumflex coronary artery) increased by 19.3% (3.21 ± 0.28 mm) after 5 min of USD exposure. After a 90-min observation period there was a return to baseline values (p = NS). Intracoronary nitroglycerin (NTG) administered to five dogs revealed a similar magnitude of vasodilation as USD. CONCLUSIONS: Noninvasive, transthoracic low-frequency USD energy results in coronary artery vasodilation within seconds of exposure. The vasodilation is reversible and is similar in magnitude to that induced by NTG. Further evaluation is needed to assess its potential applications in humans.