Graphviz, changing the size of edge

How to change the size of edge in dot (graphviz)? I would like to make some edges "bolded".

I wanted to supplement shuvalov's answer. penwidth is indeed the correct command. Additionally, in shuvalov's answer penwidth is both a node and an edge property--also correct.

The distinction i wanted to make:

• penwidth, when used as a node property (e.g., "NodeA" [penwidth = 5]) affects the border line weight for that node

• penwidth, when used as a edge property affects the line weight of the edge (default value is "1", specifying penwidth=2 will make the edge appear in bold type

• if you want to change the line weight of an edge, you do not need to change penwidth for the two nodes connected by that edge (as shuvalev's answer might suggest)

• for a directed graph (the edges have a direction) you might also wish to change the size/weight of the arrowhead and arrowtail, along with the edge weight, so that all three remain proportional

• the length of an edge can be changed by setting the weight property, as elsewhere, the default value is 1.0; increasing that value increases the cost of stretching this edge during rendering (i.e., the drawing algorithm applies a higher penalty to solutions in which this edge is longer); notice that the edge from 1 to 4 is shorter than the edge from 1 to 2.

The following code should illustrate all of this. The rendered graph is shown below the code.

digraph {
    /* declare the node & style them */
    "Node 1" [shape=diamond, penwidth=3, style=filled, fillcolor="#FCD975"];
    "Node 2" [style=filled,fillcolor="#9ACEEB" ];
    "Node 3" [shape=diamond, style=filled, fillcolor="#FCD975" ];
    "Node 4" [style=filled, fillcolor="#9ACEEB" ]

    /* declare the edges & style them */
    "Node 1" -> "Node 2" [dir=none, weight=1, penwidth=3] ;
    "Node 1" -> "Node 3" [dir=none, color="#9ACEEB"] ;
    "Node 1" -> "Node 4" [arrowsize=.5, weight=2.]
}

try this:

"NodeA" [ penwidth = 5]
"NodeB" [ penwidth = 5]
NodeA->NodeB [ penwidth = 3]