Ultrasonic imaging to receive a signal from contrast agent microbubbles in arterioles of a myocardium, without being masked by a signal from microbubbles in capillaries of the myocardium. For example, high power ultrasonic energy is emitted to destroy microbubbles in the arterioles and capillaries. A time delay passes from the destruction. The time delay is sufficiently long to allow the arterioles to refill with microbubbles and sufficiently short so that the capillaries do not completely refill with microbubbles. Ultrasonic imaging is then performed to receive a signal between harmonics from the microbubbles refilled in the arterioles. Various other destructive and non-destructive imaging techniques are disclosed.