Ultrasound probe systems and methods for using an ultrasound probe to assist during treatment of conditions of the human heart are provided. The method may comprise loading a medical instrument into a guide fastened to the ultrasound probe. The ultrasound probe may be inserted into a patient by way of an incision. The distal end of the ultrasound probe may be navigated to a location adjacent to an exterior surface of the heart. A treatment site may be identified on the exterior surface of the heart based on images obtained from an ultrasound transducer disposed within a distal end of the ultrasound probe. The medical instrument may be advanced within the guide to the treatment site and the medical instrument used for treatment. After treatment, the medical instrument may be withdrawn from the treatment site.