It is not clear what you want to plot?
format long
set(0,'DefaultAxesFontSize',20);
figure;
H1_struct = load('H_H(1).mat', 'x');
H1_x = H1_struct.x;
H2_struct = load('H_H(2).mat', 'x');
H2_x = H2_struct.x;
whos
subplot(2,1,1);
plot(H1_x(4,:), H1_x(5,:)); title('H1 x 4 vs 5');
subplot(2,1,2);
plot(H2_x(4,:), H2_x(5,:)); title('H2 x 4 vs 5');