Methods and apparatus are provided for medical ultrasound imaging. An ultrasound beam is scanned in a fast scan direction and is scanned in a slow scan direction concurrently with scanning in the fast scan direction. During scanning of the ultrasound beam, ultrasound data samples, representative of two-dimensional slices of a volume of interest in a patient, are acquired at different points in the slow scan direction and at different times in the patient's cardiac cycle. Scanning in the slow scan direction is controlled relative to the patient's cardiac cycle so that the acquired data samples have a desired spatial distribution over the volume of interest and a desired temporal distribution over the patient's cardiac cycle. The acquired data samples are converted to three-dimensional image data sets which represent the volume of interest at different times in the patient's cardiac cycle. Scanning in the slow scan direction may be controlled by starting scanning at uniformly-spaced time intervals relative to the patient's cardiac cycle.