Heart murmur. Heart murmurs are heart sounds produced when blood flows across one of the heart valves that are loud enough to be heard with a stethoscope. There are two types of murmurs. A functional murmur or physiologic murmur is a heart murmur that is primarily due to physiologic conditions outside the heart. Other types of murmurs are due to structural defects in the heart itself.
Voyager 2 passed Neptune in the summer of 1989, the first spacecraft to observe that planet. Passing about 3,000 miles above Neptune's north pole, Voyager 2 made its closest approach to any planet since it left Earth 12 years earlier.
The 10 greatest space probes ever flown. Dozens of spacecraft have been sent on interplanetary missions since the 1962 launch of the Mariner 2 mission to Venus, the first spacecraft to visit another planet. But some have made more of an impact-on science and the public imagination-than others.