How can I correct the error "Undefined function 'conv2' for input arguments of type 'struct" by using function WAVEDEC?

I am doing my project on ECG signal processing. For that I have to do 4th level wavelet decomposition on the ECG signal. But I am getting errors and not able to proceed. First I loaded a mat file from Physionet Challenge 2011 Test Set B Database to the variable 's' and then called the wavedec function on the variable 's'. But I am getting an error like

*Undefined function 'conv2' for input arguments of type 'struct'.

Error in wconv1 (line 16) y = conv2(x(:)',f(:)',shape);

Error in dwt (line 76) z = wconv1(y,Lo_D,'valid');

Error in wavedec (line 46) [x,d] = dwt(x,Lo_D,Hi_D); % decomposition*

The code I have written is included below

[fname path]=uigetfile('1026580m.mat'); fname=strcat(path,fname); s=load('1026580m.mat'); [c,l]=wavedec(s,4,'db4');

Kindly help me. I am stuck here.