Full text
PDF
. 1956 Apr;18(2):248–250. doi: 10.1136/hrt.18.2.248
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.