Q:

Heatmap R: how to remove dashed lines

I'm new to heatmap. I've data which looks like:
Dat       A        B        C        D        E
A    100       30.3      0       55.71    45.78
B     12.85   100       72.85    12.64    98.51
C      0       27.85   100       82.28     3.07
D     23.71    30.64    40.28   100        6.33
E     25.25    85       52.36    36.33   100

R code:
pdf("hh.pdf")
library(gplots)
data = read.table("file.txt", header=T, row.names=1)
heatmap.2(as.matrix(data))
dev.off()

When I plot heatmap with above data, it is Okay, with those grid lines. But when I get row count as 100 or in that range, plot is barely visible. Plot is covered with dash-dash vertical lines.
I want to get rid of those annoying lines. 
I've saved in .png format, but again, I get same lines.
I have checked heatmap.2 (gplots package) - how to remove annoying lines in some cells?
Using R 3.0.2 

A:

 pdf("hh.pdf")
 library(gplots)
 data = read.table(text="Dat       A        B        C        D        E
 A    100       30.3      0       55.71    45.78
 B     12.85   100       72.85    12.64    98.51
 C      0       27.85   100       82.28     3.07
 D     23.71    30.64    40.28   100        6.33
 E     25.25    85       52.36    36.33   100", header=T, row.names=1)

 heatmap.2(as.matrix(data), tracecol=NA)

