Atherosclerotic plaque and blood vessels may be stabilized by directing vibrational energy, typically ultrasonic energy, into the adjacent blood vessel wall. Application of the vibrational energy, optionally in combination with growth factors, growth factor genes, or other substances which enhance growth instability of a fibrotic cap over the plaque, will reduce the risk of rupture of unstable plaque and inhibit the conversion of stable plaque into unstable plaque.